diff --git a/packages/react-devtools-shared/src/backend/renderer.js b/packages/react-devtools-shared/src/backend/renderer.js
index b1e5dac527e61..803ef4b76b549 100644
--- a/packages/react-devtools-shared/src/backend/renderer.js
+++ b/packages/react-devtools-shared/src/backend/renderer.js
@@ -225,7 +225,8 @@ export function getInternalReactConstants(version: string): {
       HostSingleton: 27, // Same as above
       HostText: 6,
       IncompleteClassComponent: 17,
-      IndeterminateComponent: 2,
+      IncompleteFunctionComponent: 28,
+      IndeterminateComponent: 2, // removed in 19.0.0
       LazyComponent: 16,
       LegacyHiddenComponent: 23,
       MemoComponent: 14,
@@ -259,6 +260,7 @@ export function getInternalReactConstants(version: string): {
       HostSingleton: -1, // Doesn't exist yet
       HostText: 6,
       IncompleteClassComponent: 17,
+      IncompleteFunctionComponent: -1, // Doesn't exist yet
       IndeterminateComponent: 2,
       LazyComponent: 16,
       LegacyHiddenComponent: 24,
@@ -292,6 +294,7 @@ export function getInternalReactConstants(version: string): {
       HostSingleton: -1, // Doesn't exist yet
       HostText: 6,
       IncompleteClassComponent: 17,
+      IncompleteFunctionComponent: -1, // Doesn't exist yet
       IndeterminateComponent: 2,
       LazyComponent: 16,
       LegacyHiddenComponent: -1,
@@ -325,6 +328,7 @@ export function getInternalReactConstants(version: string): {
       HostSingleton: -1, // Doesn't exist yet
       HostText: 8,
       IncompleteClassComponent: -1, // Doesn't exist yet
+      IncompleteFunctionComponent: -1, // Doesn't exist yet
       IndeterminateComponent: 4,
       LazyComponent: -1, // Doesn't exist yet
       LegacyHiddenComponent: -1,
@@ -358,6 +362,7 @@ export function getInternalReactConstants(version: string): {
       HostSingleton: -1, // Doesn't exist yet
       HostText: 6,
       IncompleteClassComponent: -1, // Doesn't exist yet
+      IncompleteFunctionComponent: -1, // Doesn't exist yet
       IndeterminateComponent: 0,
       LazyComponent: -1, // Doesn't exist yet
       LegacyHiddenComponent: -1,
@@ -391,6 +396,7 @@ export function getInternalReactConstants(version: string): {
     CacheComponent,
     ClassComponent,
     IncompleteClassComponent,
+    IncompleteFunctionComponent,
     FunctionComponent,
     IndeterminateComponent,
     ForwardRef,
@@ -459,6 +465,7 @@ export function getInternalReactConstants(version: string): {
         return 'Cache';
       case ClassComponent:
       case IncompleteClassComponent:
+      case IncompleteFunctionComponent:
       case FunctionComponent:
       case IndeterminateComponent:
         return getDisplayName(resolvedType);
@@ -624,6 +631,7 @@ export function attach(
     HostComponent,
     HostText,
     IncompleteClassComponent,
+    IncompleteFunctionComponent,
     IndeterminateComponent,
     LegacyHiddenComponent,
     MemoComponent,
@@ -1061,6 +1069,7 @@ export function attach(
       case ClassComponent:
       case IncompleteClassComponent:
         return ElementTypeClass;
+      case IncompleteFunctionComponent:
       case FunctionComponent:
       case IndeterminateComponent:
         return ElementTypeFunction;
@@ -3059,6 +3068,7 @@ export function attach(
     switch (tag) {
       case ClassComponent:
       case IncompleteClassComponent:
+      case IncompleteFunctionComponent:
       case IndeterminateComponent:
       case FunctionComponent:
         global.$type = type;
@@ -3193,6 +3203,7 @@ export function attach(
       tag === ClassComponent ||
       tag === FunctionComponent ||
       tag === IncompleteClassComponent ||
+      tag === IncompleteFunctionComponent ||
       tag === IndeterminateComponent ||
       tag === MemoComponent ||
       tag === ForwardRef ||
@@ -3540,6 +3551,7 @@ export function attach(
       case IndeterminateComponent:
         global.$r = stateNode;
         break;
+      case IncompleteFunctionComponent:
       case FunctionComponent:
         global.$r = {
           hooks,
diff --git a/packages/react-devtools-shared/src/backend/types.js b/packages/react-devtools-shared/src/backend/types.js
index df45122f6314f..c006cf53e3d5b 100644
--- a/packages/react-devtools-shared/src/backend/types.js
+++ b/packages/react-devtools-shared/src/backend/types.js
@@ -58,6 +58,7 @@ export type WorkTagMap = {
   HostSingleton: WorkTag,
   HostText: WorkTag,
   IncompleteClassComponent: WorkTag,
+  IncompleteFunctionComponent: WorkTag,
   IndeterminateComponent: WorkTag,
   LazyComponent: WorkTag,
   LegacyHiddenComponent: WorkTag,
diff --git a/packages/react-dom/src/__tests__/ReactCompositeComponent-test.js b/packages/react-dom/src/__tests__/ReactCompositeComponent-test.js
index 5959cdefccfe3..2e56a911a0c38 100644
--- a/packages/react-dom/src/__tests__/ReactCompositeComponent-test.js
+++ b/packages/react-dom/src/__tests__/ReactCompositeComponent-test.js
@@ -223,23 +223,16 @@ describe('ReactCompositeComponent', () => {
     const el = document.createElement('div');
     const root = ReactDOMClient.createRoot(el);
     await expect(async () => {
-      await expect(async () => {
-        await act(() => {
-          root.render(<Child test="test" />);
-        });
-      }).rejects.toThrow(
-        'Objects are not valid as a React child (found: object with keys {render}).',
-      );
-    }).toErrorDev(
-      'Warning: The <Child /> component appears to be a function component that returns a class instance. ' +
-        'Change Child to a class that extends React.Component instead. ' +
-        "If you can't use a class try assigning the prototype on the function as a workaround. " +
-        '`Child.prototype = React.Component.prototype`. ' +
-        "Don't use an arrow function since it cannot be called with `new` by React.",
+      await act(() => {
+        root.render(<Child test="test" />);
+      });
+    }).rejects.toThrow(
+      'Objects are not valid as a React child (found: object with keys {render}).',
     );
 
     expect(el.textContent).toBe('');
   });
+
   it('should use default values for undefined props', async () => {
     class Component extends React.Component {
       static defaultProps = {prop: 'testKey'};
diff --git a/packages/react-reconciler/src/ReactFiber.js b/packages/react-reconciler/src/ReactFiber.js
index 5b8dc06fb5f69..d676966907826 100644
--- a/packages/react-reconciler/src/ReactFiber.js
+++ b/packages/react-reconciler/src/ReactFiber.js
@@ -41,7 +41,6 @@ import {
 import {NoFlags, Placement, StaticMask} from './ReactFiberFlags';
 import {ConcurrentRoot} from './ReactRootTags';
 import {
-  IndeterminateComponent,
   ClassComponent,
   HostRoot,
   HostComponent,
@@ -245,19 +244,10 @@ export function isSimpleFunctionComponent(type: any): boolean {
   );
 }
 
-export function resolveLazyComponentTag(Component: Function): WorkTag {
-  if (typeof Component === 'function') {
-    return shouldConstruct(Component) ? ClassComponent : FunctionComponent;
-  } else if (Component !== undefined && Component !== null) {
-    const $$typeof = Component.$$typeof;
-    if ($$typeof === REACT_FORWARD_REF_TYPE) {
-      return ForwardRef;
-    }
-    if ($$typeof === REACT_MEMO_TYPE) {
-      return MemoComponent;
-    }
-  }
-  return IndeterminateComponent;
+export function isFunctionClassComponent(
+  type: (...args: Array<any>) => mixed,
+): boolean {
+  return shouldConstruct(type);
 }
 
 // This is used to create an alternate fiber to do work on.
@@ -348,7 +338,6 @@ export function createWorkInProgress(current: Fiber, pendingProps: any): Fiber {
     workInProgress._debugInfo = current._debugInfo;
     workInProgress._debugNeedsRemount = current._debugNeedsRemount;
     switch (workInProgress.tag) {
-      case IndeterminateComponent:
       case FunctionComponent:
       case SimpleMemoComponent:
         workInProgress.type = resolveFunctionForHotReloading(current.type);
@@ -489,7 +478,7 @@ export function createFiberFromTypeAndProps(
   mode: TypeOfMode,
   lanes: Lanes,
 ): Fiber {
-  let fiberTag = IndeterminateComponent;
+  let fiberTag = FunctionComponent;
   // The resolved type is set if we know what the final type will be. I.e. it's not lazy.
   let resolvedType = type;
   if (typeof type === 'function') {
diff --git a/packages/react-reconciler/src/ReactFiberBeginWork.js b/packages/react-reconciler/src/ReactFiberBeginWork.js
index 9e745a69c5c83..fbf7988cdea78 100644
--- a/packages/react-reconciler/src/ReactFiberBeginWork.js
+++ b/packages/react-reconciler/src/ReactFiberBeginWork.js
@@ -46,7 +46,6 @@ import {
   setIsStrictModeForDevtools,
 } from './ReactFiberDevToolsHook';
 import {
-  IndeterminateComponent,
   FunctionComponent,
   ClassComponent,
   HostRoot,
@@ -67,6 +66,7 @@ import {
   SimpleMemoComponent,
   LazyComponent,
   IncompleteClassComponent,
+  IncompleteFunctionComponent,
   ScopeComponent,
   OffscreenComponent,
   LegacyHiddenComponent,
@@ -114,7 +114,12 @@ import shallowEqual from 'shared/shallowEqual';
 import getComponentNameFromFiber from 'react-reconciler/src/getComponentNameFromFiber';
 import getComponentNameFromType from 'shared/getComponentNameFromType';
 import ReactStrictModeWarnings from './ReactStrictModeWarnings';
-import {REACT_LAZY_TYPE, getIteratorFn} from 'shared/ReactSymbols';
+import {
+  REACT_LAZY_TYPE,
+  REACT_FORWARD_REF_TYPE,
+  REACT_MEMO_TYPE,
+  getIteratorFn,
+} from 'shared/ReactSymbols';
 import {
   getCurrentFiberOwnerNameInDevOrNull,
   setIsRendering,
@@ -242,12 +247,12 @@ import {
 } from './ReactFiberClassComponent';
 import {resolveDefaultProps} from './ReactFiberLazyComponent';
 import {
-  resolveLazyComponentTag,
   createFiberFromTypeAndProps,
   createFiberFromFragment,
   createFiberFromOffscreen,
   createWorkInProgress,
   isSimpleFunctionComponent,
+  isFunctionClassComponent,
 } from './ReactFiber';
 import {
   retryDehydratedSuspenseBoundary,
@@ -303,7 +308,6 @@ export const SelectiveHydrationException: mixed = new Error(
 let didReceiveUpdate: boolean = false;
 
 let didWarnAboutBadClass;
-let didWarnAboutModulePatternComponent;
 let didWarnAboutContextTypeOnFunctionComponent;
 let didWarnAboutGetDerivedStateOnFunctionComponent;
 let didWarnAboutFunctionRefs;
@@ -314,7 +318,6 @@ let didWarnAboutDefaultPropsOnFunctionComponent;
 
 if (__DEV__) {
   didWarnAboutBadClass = ({}: {[string]: boolean});
-  didWarnAboutModulePatternComponent = ({}: {[string]: boolean});
   didWarnAboutContextTypeOnFunctionComponent = ({}: {[string]: boolean});
   didWarnAboutGetDerivedStateOnFunctionComponent = ({}: {[string]: boolean});
   didWarnAboutFunctionRefs = ({}: {[string]: boolean});
@@ -1044,6 +1047,26 @@ function markRef(current: Fiber | null, workInProgress: Fiber) {
   }
 }
 
+function mountIncompleteFunctionComponent(
+  _current: null | Fiber,
+  workInProgress: Fiber,
+  Component: any,
+  nextProps: any,
+  renderLanes: Lanes,
+) {
+  resetSuspendedCurrentOnMountInLegacyMode(_current, workInProgress);
+
+  workInProgress.tag = FunctionComponent;
+
+  return updateFunctionComponent(
+    null,
+    workInProgress,
+    Component,
+    nextProps,
+    renderLanes,
+  );
+}
+
 function updateFunctionComponent(
   current: null | Fiber,
   workInProgress: Fiber,
@@ -1051,6 +1074,43 @@ function updateFunctionComponent(
   nextProps: any,
   renderLanes: Lanes,
 ) {
+  if (__DEV__) {
+    if (
+      Component.prototype &&
+      typeof Component.prototype.render === 'function'
+    ) {
+      const componentName = getComponentNameFromType(Component) || 'Unknown';
+
+      if (!didWarnAboutBadClass[componentName]) {
+        console.error(
+          "The <%s /> component appears to have a render method, but doesn't extend React.Component. " +
+            'This is likely to cause errors. Change %s to extend React.Component instead.',
+          componentName,
+          componentName,
+        );
+        didWarnAboutBadClass[componentName] = true;
+      }
+    }
+
+    if (workInProgress.mode & StrictLegacyMode) {
+      ReactStrictModeWarnings.recordLegacyContextWarning(workInProgress, null);
+    }
+
+    if (current === null) {
+      // Some validations were previously done in mountIndeterminateComponent however and are now run
+      // in updateFuntionComponent but only on mount
+      validateFunctionComponentInDev(workInProgress, workInProgress.type);
+
+      if (disableLegacyContext && Component.contextTypes) {
+        console.error(
+          '%s uses the legacy contextTypes API which was removed in React 19. ' +
+            'Use React.createContext() with React.useContext() instead.',
+          getComponentNameFromType(Component) || 'Unknown',
+        );
+      }
+    }
+  }
+
   let context;
   if (!disableLegacyContext) {
     const unmaskedContext = getUnmaskedContext(workInProgress, Component, true);
@@ -1697,64 +1757,64 @@ function mountLazyComponent(
   let Component = init(payload);
   // Store the unwrapped component in the type.
   workInProgress.type = Component;
-  const resolvedTag = (workInProgress.tag = resolveLazyComponentTag(Component));
+
   const resolvedProps = resolveDefaultProps(Component, props);
-  let child;
-  switch (resolvedTag) {
-    case FunctionComponent: {
+  if (typeof Component === 'function') {
+    if (isFunctionClassComponent(Component)) {
+      workInProgress.tag = ClassComponent;
       if (__DEV__) {
-        validateFunctionComponentInDev(workInProgress, Component);
         workInProgress.type = Component =
-          resolveFunctionForHotReloading(Component);
+          resolveClassForHotReloading(Component);
       }
-      child = updateFunctionComponent(
+      return updateClassComponent(
         null,
         workInProgress,
         Component,
         resolvedProps,
         renderLanes,
       );
-      return child;
-    }
-    case ClassComponent: {
+    } else {
+      workInProgress.tag = FunctionComponent;
       if (__DEV__) {
+        validateFunctionComponentInDev(workInProgress, Component);
         workInProgress.type = Component =
-          resolveClassForHotReloading(Component);
+          resolveFunctionForHotReloading(Component);
       }
-      child = updateClassComponent(
+      return updateFunctionComponent(
         null,
         workInProgress,
         Component,
         resolvedProps,
         renderLanes,
       );
-      return child;
     }
-    case ForwardRef: {
+  } else if (Component !== undefined && Component !== null) {
+    const $$typeof = Component.$$typeof;
+    if ($$typeof === REACT_FORWARD_REF_TYPE) {
+      workInProgress.tag = ForwardRef;
       if (__DEV__) {
         workInProgress.type = Component =
           resolveForwardRefForHotReloading(Component);
       }
-      child = updateForwardRef(
+      return updateForwardRef(
         null,
         workInProgress,
         Component,
         resolvedProps,
         renderLanes,
       );
-      return child;
-    }
-    case MemoComponent: {
-      child = updateMemoComponent(
+    } else if ($$typeof === REACT_MEMO_TYPE) {
+      workInProgress.tag = MemoComponent;
+      return updateMemoComponent(
         null,
         workInProgress,
         Component,
         resolveDefaultProps(Component.type, resolvedProps), // The inner type can have defaults too
         renderLanes,
       );
-      return child;
     }
   }
+
   let hint = '';
   if (__DEV__) {
     if (
@@ -1814,133 +1874,6 @@ function mountIncompleteClassComponent(
   );
 }
 
-function mountIndeterminateComponent(
-  _current: null | Fiber,
-  workInProgress: Fiber,
-  Component: $FlowFixMe,
-  renderLanes: Lanes,
-) {
-  resetSuspendedCurrentOnMountInLegacyMode(_current, workInProgress);
-
-  const props = workInProgress.pendingProps;
-  let context;
-  if (!disableLegacyContext) {
-    const unmaskedContext = getUnmaskedContext(
-      workInProgress,
-      Component,
-      false,
-    );
-    context = getMaskedContext(workInProgress, unmaskedContext);
-  }
-
-  prepareToReadContext(workInProgress, renderLanes);
-  let value;
-  let hasId;
-
-  if (enableSchedulingProfiler) {
-    markComponentRenderStarted(workInProgress);
-  }
-  if (__DEV__) {
-    if (
-      Component.prototype &&
-      typeof Component.prototype.render === 'function'
-    ) {
-      const componentName = getComponentNameFromType(Component) || 'Unknown';
-
-      if (!didWarnAboutBadClass[componentName]) {
-        console.error(
-          "The <%s /> component appears to have a render method, but doesn't extend React.Component. " +
-            'This is likely to cause errors. Change %s to extend React.Component instead.',
-          componentName,
-          componentName,
-        );
-        didWarnAboutBadClass[componentName] = true;
-      }
-    }
-
-    if (workInProgress.mode & StrictLegacyMode) {
-      ReactStrictModeWarnings.recordLegacyContextWarning(workInProgress, null);
-    }
-
-    setIsRendering(true);
-    ReactCurrentOwner.current = workInProgress;
-    value = renderWithHooks(
-      null,
-      workInProgress,
-      Component,
-      props,
-      context,
-      renderLanes,
-    );
-    hasId = checkDidRenderIdHook();
-    setIsRendering(false);
-  } else {
-    value = renderWithHooks(
-      null,
-      workInProgress,
-      Component,
-      props,
-      context,
-      renderLanes,
-    );
-    hasId = checkDidRenderIdHook();
-  }
-  if (enableSchedulingProfiler) {
-    markComponentRenderStopped();
-  }
-
-  // React DevTools reads this flag.
-  workInProgress.flags |= PerformedWork;
-
-  if (__DEV__) {
-    // Support for module components is deprecated and is removed behind a flag.
-    // Whether or not it would crash later, we want to show a good message in DEV first.
-    if (
-      typeof value === 'object' &&
-      value !== null &&
-      typeof value.render === 'function' &&
-      value.$$typeof === undefined
-    ) {
-      const componentName = getComponentNameFromType(Component) || 'Unknown';
-      if (!didWarnAboutModulePatternComponent[componentName]) {
-        console.error(
-          'The <%s /> component appears to be a function component that returns a class instance. ' +
-            'Change %s to a class that extends React.Component instead. ' +
-            "If you can't use a class try assigning the prototype on the function as a workaround. " +
-            "`%s.prototype = React.Component.prototype`. Don't use an arrow function since it " +
-            'cannot be called with `new` by React.',
-          componentName,
-          componentName,
-          componentName,
-        );
-        didWarnAboutModulePatternComponent[componentName] = true;
-      }
-    }
-  }
-
-  // Proceed under the assumption that this is a function component
-  workInProgress.tag = FunctionComponent;
-  if (__DEV__) {
-    if (disableLegacyContext && Component.contextTypes) {
-      console.error(
-        '%s uses the legacy contextTypes API which was removed in React 19. ' +
-          'Use React.createContext() with React.useContext() instead.',
-        getComponentNameFromType(Component) || 'Unknown',
-      );
-    }
-  }
-
-  if (getIsHydrating() && hasId) {
-    pushMaterializedTreeId(workInProgress);
-  }
-
-  reconcileChildren(null, workInProgress, value, renderLanes);
-  if (__DEV__) {
-    validateFunctionComponentInDev(workInProgress, Component);
-  }
-  return workInProgress.child;
-}
-
 function validateFunctionComponentInDev(workInProgress: Fiber, Component: any) {
   if (__DEV__) {
     if (Component) {
@@ -3972,14 +3905,6 @@ function beginWork(
   workInProgress.lanes = NoLanes;
 
   switch (workInProgress.tag) {
-    case IndeterminateComponent: {
-      return mountIndeterminateComponent(
-        current,
-        workInProgress,
-        workInProgress.type,
-        renderLanes,
-      );
-    }
     case LazyComponent: {
       const elementType = workInProgress.elementType;
       return mountLazyComponent(
@@ -4102,6 +4027,21 @@ function beginWork(
         renderLanes,
       );
     }
+    case IncompleteFunctionComponent: {
+      const Component = workInProgress.type;
+      const unresolvedProps = workInProgress.pendingProps;
+      const resolvedProps =
+        workInProgress.elementType === Component
+          ? unresolvedProps
+          : resolveDefaultProps(Component, unresolvedProps);
+      return mountIncompleteFunctionComponent(
+        current,
+        workInProgress,
+        Component,
+        resolvedProps,
+        renderLanes,
+      );
+    }
     case SuspenseListComponent: {
       return updateSuspenseListComponent(current, workInProgress, renderLanes);
     }
diff --git a/packages/react-reconciler/src/ReactFiberClassComponent.js b/packages/react-reconciler/src/ReactFiberClassComponent.js
index b64f9f9e626c8..47d1c3cfee476 100644
--- a/packages/react-reconciler/src/ReactFiberClassComponent.js
+++ b/packages/react-reconciler/src/ReactFiberClassComponent.js
@@ -569,16 +569,6 @@ function checkClassInstance(workInProgress: Fiber, ctor: any, newProps: any) {
   }
 }
 
-function adoptClassInstance(workInProgress: Fiber, instance: any): void {
-  instance.updater = classComponentUpdater;
-  workInProgress.stateNode = instance;
-  // The instance needs access to the fiber so that it can schedule updates
-  setInstance(instance, workInProgress);
-  if (__DEV__) {
-    instance._reactInternalInstance = fakeInternalInstance;
-  }
-}
-
 function constructClassInstance(
   workInProgress: Fiber,
   ctor: any,
@@ -659,7 +649,13 @@ function constructClassInstance(
     instance.state !== null && instance.state !== undefined
       ? instance.state
       : null);
-  adoptClassInstance(workInProgress, instance);
+  instance.updater = classComponentUpdater;
+  workInProgress.stateNode = instance;
+  // The instance needs access to the fiber so that it can schedule updates
+  setInstance(instance, workInProgress);
+  if (__DEV__) {
+    instance._reactInternalInstance = fakeInternalInstance;
+  }
 
   if (__DEV__) {
     if (typeof ctor.getDerivedStateFromProps === 'function' && state === null) {
diff --git a/packages/react-reconciler/src/ReactFiberCompleteWork.js b/packages/react-reconciler/src/ReactFiberCompleteWork.js
index 89044182672ad..01087e3696279 100644
--- a/packages/react-reconciler/src/ReactFiberCompleteWork.js
+++ b/packages/react-reconciler/src/ReactFiberCompleteWork.js
@@ -45,7 +45,6 @@ import {
 import {now} from './Scheduler';
 
 import {
-  IndeterminateComponent,
   FunctionComponent,
   ClassComponent,
   HostRoot,
@@ -66,6 +65,7 @@ import {
   SimpleMemoComponent,
   LazyComponent,
   IncompleteClassComponent,
+  IncompleteFunctionComponent,
   ScopeComponent,
   OffscreenComponent,
   LegacyHiddenComponent,
@@ -949,10 +949,10 @@ function completeWork(
   // for hydration.
   popTreeContext(workInProgress);
   switch (workInProgress.tag) {
-    case IndeterminateComponent:
     case LazyComponent:
     case SimpleMemoComponent:
     case FunctionComponent:
+    case IncompleteFunctionComponent:
     case ForwardRef:
     case Fragment:
     case Mode:
diff --git a/packages/react-reconciler/src/ReactFiberComponentStack.js b/packages/react-reconciler/src/ReactFiberComponentStack.js
index 36e22e8a9b1f2..f292cb51d10b4 100644
--- a/packages/react-reconciler/src/ReactFiberComponentStack.js
+++ b/packages/react-reconciler/src/ReactFiberComponentStack.js
@@ -17,7 +17,6 @@ import {
   SuspenseComponent,
   SuspenseListComponent,
   FunctionComponent,
-  IndeterminateComponent,
   ForwardRef,
   SimpleMemoComponent,
   ClassComponent,
@@ -47,7 +46,6 @@ function describeFiber(fiber: Fiber): string {
     case SuspenseListComponent:
       return describeBuiltInComponentFrame('SuspenseList', owner);
     case FunctionComponent:
-    case IndeterminateComponent:
     case SimpleMemoComponent:
       return describeFunctionComponentFrame(fiber.type, owner);
     case ForwardRef:
diff --git a/packages/react-reconciler/src/ReactFiberHydrationDiffs.js b/packages/react-reconciler/src/ReactFiberHydrationDiffs.js
index 812d9d046a533..021da8abf33f1 100644
--- a/packages/react-reconciler/src/ReactFiberHydrationDiffs.js
+++ b/packages/react-reconciler/src/ReactFiberHydrationDiffs.js
@@ -17,7 +17,6 @@ import {
   SuspenseComponent,
   SuspenseListComponent,
   FunctionComponent,
-  IndeterminateComponent,
   ForwardRef,
   SimpleMemoComponent,
   ClassComponent,
@@ -87,7 +86,6 @@ function describeFiberType(fiber: Fiber): null | string {
     case SuspenseListComponent:
       return 'SuspenseList';
     case FunctionComponent:
-    case IndeterminateComponent:
     case SimpleMemoComponent:
       const fn = fiber.type;
       return fn.displayName || fn.name || null;
diff --git a/packages/react-reconciler/src/ReactFiberThrow.js b/packages/react-reconciler/src/ReactFiberThrow.js
index 3bb54f73e80d6..5b40a872b1f85 100644
--- a/packages/react-reconciler/src/ReactFiberThrow.js
+++ b/packages/react-reconciler/src/ReactFiberThrow.js
@@ -20,6 +20,7 @@ import {
   ClassComponent,
   HostRoot,
   IncompleteClassComponent,
+  IncompleteFunctionComponent,
   FunctionComponent,
   ForwardRef,
   SimpleMemoComponent,
@@ -262,6 +263,13 @@ function markSuspenseBoundaryShouldCapture(
           update.tag = ForceUpdate;
           enqueueUpdate(sourceFiber, update, SyncLane);
         }
+      } else if (sourceFiber.tag === FunctionComponent) {
+        const currentSourceFiber = sourceFiber.alternate;
+        if (currentSourceFiber === null) {
+          // This is a new mount. Change the tag so it's not mistaken for a
+          // completed function component.
+          sourceFiber.tag = IncompleteFunctionComponent;
+        }
       }
 
       // The source fiber did not complete. Mark it with Sync priority to
diff --git a/packages/react-reconciler/src/ReactFiberWorkLoop.js b/packages/react-reconciler/src/ReactFiberWorkLoop.js
index ea8869a4a8c13..2570f857c7d2d 100644
--- a/packages/react-reconciler/src/ReactFiberWorkLoop.js
+++ b/packages/react-reconciler/src/ReactFiberWorkLoop.js
@@ -90,7 +90,6 @@ import {
 } from './ReactTypeOfMode';
 import {
   HostRoot,
-  IndeterminateComponent,
   ClassComponent,
   SuspenseComponent,
   SuspenseListComponent,
@@ -2395,12 +2394,6 @@ function replaySuspendedUnitOfWork(unitOfWork: Fiber): void {
     startProfilerTimer(unitOfWork);
   }
   switch (unitOfWork.tag) {
-    case IndeterminateComponent: {
-      // Because it suspended with `use`, we can assume it's a
-      // function component.
-      unitOfWork.tag = FunctionComponent;
-      // Fallthrough to the next branch.
-    }
     case SimpleMemoComponent:
     case FunctionComponent: {
       // Resolve `defaultProps`. This logic is copied from `beginWork`.
@@ -3807,7 +3800,6 @@ export function warnAboutUpdateOnNotYetMountedFiberInDEV(fiber: Fiber) {
 
     const tag = fiber.tag;
     if (
-      tag !== IndeterminateComponent &&
       tag !== HostRoot &&
       tag !== ClassComponent &&
       tag !== FunctionComponent &&
diff --git a/packages/react-reconciler/src/ReactWorkTags.js b/packages/react-reconciler/src/ReactWorkTags.js
index 8e928d671dc87..a4d4eb1751548 100644
--- a/packages/react-reconciler/src/ReactWorkTags.js
+++ b/packages/react-reconciler/src/ReactWorkTags.js
@@ -35,11 +35,11 @@ export type WorkTag =
   | 24
   | 25
   | 26
-  | 27;
+  | 27
+  | 28;
 
 export const FunctionComponent = 0;
 export const ClassComponent = 1;
-export const IndeterminateComponent = 2; // Before we know whether it is function or class
 export const HostRoot = 3; // Root of a host tree. Could be nested inside another node.
 export const HostPortal = 4; // A subtree. Could be an entry point to a different renderer.
 export const HostComponent = 5;
@@ -64,3 +64,4 @@ export const CacheComponent = 24;
 export const TracingMarkerComponent = 25;
 export const HostHoistable = 26;
 export const HostSingleton = 27;
+export const IncompleteFunctionComponent = 28;
diff --git a/packages/react-reconciler/src/__tests__/ReactSubtreeFlagsWarning-test.js b/packages/react-reconciler/src/__tests__/ReactSubtreeFlagsWarning-test.js
index 49bde67837cdf..e5d9c9c445dad 100644
--- a/packages/react-reconciler/src/__tests__/ReactSubtreeFlagsWarning-test.js
+++ b/packages/react-reconciler/src/__tests__/ReactSubtreeFlagsWarning-test.js
@@ -132,11 +132,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
 
   // @gate experimental || www
   it('regression: false positive for legacy suspense', async () => {
-    // Wrapping in memo because regular function components go through the
-    // mountIndeterminateComponent path, which acts like there's no `current`
-    // fiber even though there is. `memo` is not indeterminate, so it goes
-    // through the update path.
-    const Child = React.memo(({text}) => {
+    const Child = ({text}) => {
       // If text hasn't resolved, this will throw and exit before the passive
       // static effect flag is added by the useEffect call below.
       readText(text);
@@ -147,7 +143,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
 
       Scheduler.log(text);
       return text;
-    });
+    };
 
     function App() {
       return (
diff --git a/packages/react-reconciler/src/getComponentNameFromFiber.js b/packages/react-reconciler/src/getComponentNameFromFiber.js
index 1a8464835ce4f..9eb7fdf4f8907 100644
--- a/packages/react-reconciler/src/getComponentNameFromFiber.js
+++ b/packages/react-reconciler/src/getComponentNameFromFiber.js
@@ -18,7 +18,6 @@ import {
 import {
   FunctionComponent,
   ClassComponent,
-  IndeterminateComponent,
   HostRoot,
   HostPortal,
   HostComponent,
@@ -128,7 +127,6 @@ export default function getComponentNameFromFiber(fiber: Fiber): string | null {
     case ClassComponent:
     case FunctionComponent:
     case IncompleteClassComponent:
-    case IndeterminateComponent:
     case MemoComponent:
     case SimpleMemoComponent:
       if (typeof type === 'function') {
diff --git a/packages/react-server/src/ReactFizzServer.js b/packages/react-server/src/ReactFizzServer.js
index 788544b731e12..a06ef06e8bb2b 100644
--- a/packages/react-server/src/ReactFizzServer.js
+++ b/packages/react-server/src/ReactFizzServer.js
@@ -1410,7 +1410,6 @@ function renderClassComponent(
 }
 
 const didWarnAboutBadClass: {[string]: boolean} = {};
-const didWarnAboutModulePatternComponent: {[string]: boolean} = {};
 const didWarnAboutContextTypeOnFunctionComponent: {[string]: boolean} = {};
 const didWarnAboutGetDerivedStateOnFunctionComponent: {[string]: boolean} = {};
 let didWarnAboutReassigningProps = false;
@@ -1418,9 +1417,7 @@ const didWarnAboutDefaultPropsOnFunctionComponent: {[string]: boolean} = {};
 let didWarnAboutGenerators = false;
 let didWarnAboutMaps = false;
 
-// This would typically be a function component but we still support module pattern
-// components for some reason.
-function renderIndeterminateComponent(
+function renderFunctionComponent(
   request: Request,
   task: Task,
   keyPath: KeyNode,
@@ -1465,33 +1462,6 @@ function renderIndeterminateComponent(
   const actionStateCount = getActionStateCount();
   const actionStateMatchingIndex = getActionStateMatchingIndex();
 
-  if (__DEV__) {
-    // Support for module components is deprecated and is removed behind a flag.
-    // Whether or not it would crash later, we want to show a good message in DEV first.
-    if (
-      typeof value === 'object' &&
-      value !== null &&
-      typeof value.render === 'function' &&
-      value.$$typeof === undefined
-    ) {
-      const componentName = getComponentNameFromType(Component) || 'Unknown';
-      if (!didWarnAboutModulePatternComponent[componentName]) {
-        console.error(
-          'The <%s /> component appears to be a function component that returns a class instance. ' +
-            'Change %s to a class that extends React.Component instead. ' +
-            "If you can't use a class try assigning the prototype on the function as a workaround. " +
-            "`%s.prototype = React.Component.prototype`. Don't use an arrow function since it " +
-            'cannot be called with `new` by React.',
-          componentName,
-          componentName,
-          componentName,
-        );
-        didWarnAboutModulePatternComponent[componentName] = true;
-      }
-    }
-  }
-
-  // Proceed under the assumption that this is a function component
   if (__DEV__) {
     if (disableLegacyContext && Component.contextTypes) {
       console.error(
@@ -1817,7 +1787,7 @@ function renderElement(
       renderClassComponent(request, task, keyPath, type, props);
       return;
     } else {
-      renderIndeterminateComponent(request, task, keyPath, type, props);
+      renderFunctionComponent(request, task, keyPath, type, props);
       return;
     }
   }