diff --git a/README.md b/README.md
index 9bb2ce7f69..d94673ebcd 100644
--- a/README.md
+++ b/README.md
@@ -700,9 +700,18 @@ const ngModule = MockBuilder(MyComponent, MyModule)
 
 Provides a simple way to render anything for ease of testing directives, pipes, `@Inputs`, `@Outputs`, `@ContentChild` of a component, etc.
 
+> Please note, that `MockRender(MyComponent)` is not assignable to `ComponentFixture<MyComponent>`.
+>
+> You should use either:
+> `MockedComponentFixture<MyComponent>` or
+> `ComponentFixture<DefaultRenderComponent<MyComponent>>`.
+>
+> It happens because `MockRender` generates an additional component to render the desired thing
+> and its interface differs.
+
 It returns a `fixture` of type `MockedComponentFixture` (it extends `ComponentFixture`) with a `point` property.
-`fixture.componentInstance` belongs to the middle component for the render, that is quite useless,
-when `fixture.point` points to the debugElement of the passed component.
+`fixture.componentInstance` belongs to the middle component for the render,
+when `fixture.point` points to the debugElement of the desired component.
 
 Its type: `let fixture: MockedComponentFixture<ComponentToRender> = MockRender(ComponentToRender)`.
 
diff --git a/karma.conf.ts b/karma.conf.ts
index 2554288919..167f28d325 100644
--- a/karma.conf.ts
+++ b/karma.conf.ts
@@ -38,7 +38,7 @@ module.exports = (config: any) => {
 
     karmaTypescriptConfig: {
       include: ['karma-test-shim.ts', 'lib/**/*', 'examples/**/*', 'tests/**/*'],
-      tsconfig: 'tsconfig.json',
+      tsconfig: 'tsconfig.spec.json',
     },
   });
 };
diff --git a/lib/mock-render/mock-render.ts b/lib/mock-render/mock-render.ts
index 3659b7032e..59ae45ce0f 100644
--- a/lib/mock-render/mock-render.ts
+++ b/lib/mock-render/mock-render.ts
@@ -24,7 +24,7 @@ export interface IMockRenderOptions {
 }
 
 // tslint:disable-next-line:interface-name
-export interface MockedComponentFixture<C = any, F = undefined> extends ComponentFixture<F> {
+export interface MockedComponentFixture<C = any, F = DefaultRenderComponent<C>> extends ComponentFixture<F> {
   point: MockedDebugElement<C>;
 }
 
@@ -56,7 +56,7 @@ function MockRender<MComponent, TComponent extends { [key: string]: any }>(
 // without params we shouldn't autocomplete any keys of any types.
 function MockRender<MComponent extends Record<keyof any, any>>(
   template: Type<MComponent>
-): MockedComponentFixture<MComponent, DefaultRenderComponent<MComponent>>;
+): MockedComponentFixture<MComponent>;
 
 function MockRender<MComponent = any, TComponent extends { [key: string]: any } = { [key: string]: any }>(
   template: string,
diff --git a/tests/mock-render-mirrors-component/test.spec.ts b/tests/mock-render-mirrors-component/test.spec.ts
index d829b895fc..0d0ba8e306 100644
--- a/tests/mock-render-mirrors-component/test.spec.ts
+++ b/tests/mock-render-mirrors-component/test.spec.ts
@@ -1,5 +1,6 @@
-import { Component, EventEmitter, Input, NgModule, Output } from '@angular/core';
-import { MockBuilder, MockRender, ngMocks } from 'ng-mocks';
+import { ChangeDetectorRef, Component, EventEmitter, Input, NgModule, Output } from '@angular/core';
+import { ComponentFixture } from '@angular/core/testing';
+import { DefaultRenderComponent, MockBuilder, MockedComponentFixture, MockRender, ngMocks } from 'ng-mocks';
 import { first } from 'rxjs/operators';
 
 @Component({
@@ -23,7 +24,16 @@ export class TargetComponent {
   public var1 = '';
   public var2 = '';
 
+  // required for DefaultRenderComponent generation assertion.
+  protected readonly cdf: ChangeDetectorRef;
+  protected var3 = '';
+
+  constructor(cdf: ChangeDetectorRef) {
+    this.cdf = cdf;
+  }
+
   public test(var2: string): void {
+    this.var3 = this.var2;
     this.var2 = var2;
   }
 }
@@ -80,4 +90,42 @@ describe('mock-render-mirrors-component', () => {
     output2.triggerEventHandler('click', null);
     expect(updatedOutput2).toBe(true);
   });
+
+  it('correctly inherits types', () => {
+    // keeps the 2nd args as DefaultRenderComponent<TargetComponent>
+    const fixture1: MockedComponentFixture<TargetComponent> = MockRender(TargetComponent);
+    fixture1.componentInstance.input1 = '1';
+    fixture1.detectChanges();
+    expect(fixture1).toBeDefined();
+    expect(fixture1.componentInstance.input1).toBe('1');
+    expect(fixture1.point.componentInstance.input1).toBe('1');
+
+    // we have to provide DefaultRenderComponent in this case.
+    // the generated component isn't the same as the testing component.
+    const fixture2: ComponentFixture<DefaultRenderComponent<TargetComponent>> = MockRender(TargetComponent);
+    fixture2.componentInstance.input1 = '1';
+    fixture2.detectChanges();
+    expect(fixture2).toBeDefined();
+    expect(fixture2.componentInstance.input1).toBe('1');
+
+    // full declaration of the mocked fixture type.
+    const fixture3: MockedComponentFixture<TargetComponent, Record<'input1' | 'input3', string>> = MockRender(
+      TargetComponent,
+      {
+        input1: '1',
+        input3: '3',
+      }
+    );
+    expect(fixture3).toBeDefined();
+    expect(fixture3.componentInstance.input3).toBe('3');
+    expect(fixture3.point.componentInstance.input1).toBe('1');
+
+    // full declaration of the default fixture type.
+    const fixture4: ComponentFixture<Record<'input1' | 'input3', string>> = MockRender(TargetComponent, {
+      input1: '1',
+      input3: '3',
+    });
+    expect(fixture4).toBeDefined();
+    expect(fixture4.componentInstance.input3).toBe('3');
+  });
 });
diff --git a/tsconfig.spec.json b/tsconfig.spec.json
new file mode 100644
index 0000000000..824600dfcd
--- /dev/null
+++ b/tsconfig.spec.json
@@ -0,0 +1,6 @@
+{
+  "extends": "./tsconfig.json",
+  "files": ["index.ts", "jasmine.ts", "jest.ts"],
+  "exclude": ["e2e"],
+  "include": ["**/*.spec.ts"]
+}