diff --git a/docs/core/compatibility/corefx.md b/docs/core/compatibility/corefx.md
index eab57c37c2e5e..82cb750b2839d 100644
--- a/docs/core/compatibility/corefx.md
+++ b/docs/core/compatibility/corefx.md
@@ -11,6 +11,7 @@ The following breaking changes are documented on this page:
 
 | Breaking change | Version introduced |
 | - | :-: |
+| [Parameter names changed in RC1](#parameter-names-changed-in-rc1) | 5.0 |
 | [OSPlatform attributes renamed or removed](#osplatform-attributes-renamed-or-removed) | 5.0 |
 | [Thread.Abort is obsolete](#threadabort-is-obsolete) | 5.0 |
 | [Obsolete properties on ConsoleLoggerOptions](#obsolete-properties-on-consoleloggeroptions) | 5.0 |
@@ -49,6 +50,10 @@ The following breaking changes are documented on this page:
 
 ## .NET 5.0
 
+[!INCLUDE [reference-assembly-parameter-names-rc1](../../../includes/core-changes/corefx/5.0/reference-assembly-parameter-names-rc1.md)]
+
+***
+
 [!INCLUDE [os-platform-attributes-renamed](../../../includes/core-changes/corefx/5.0/os-platform-attributes-renamed.md)]
 
 ***
diff --git a/includes/core-changes/corefx/5.0/reference-assembly-parameter-names-rc1.md b/includes/core-changes/corefx/5.0/reference-assembly-parameter-names-rc1.md
new file mode 100644
index 0000000000000..e6b466fb496f3
--- /dev/null
+++ b/includes/core-changes/corefx/5.0/reference-assembly-parameter-names-rc1.md
@@ -0,0 +1,46 @@
+### Parameter names changed in RC1
+
+Some reference assembly parameter names have changed to match parameter names in the implementation assemblies.
+
+#### Change description
+
+In previous .NET 5.0 preview and RC versions, some [reference assembly](../../../../docs/standard/assembly/reference-assemblies.md) parameter names are different to their corresponding parameters in the implementation assembly. This can cause problems while using named arguments and reflection.
+
+In .NET 5.0 RC2, these mismatched parameter names were updated in the reference assemblies to exactly match the corresponding parameter names in the implementation assemblies.
+
+The following table shows the APIs and parameter names that changed.
+
+| API | Old parameter name | New parameter name |
+| - | - | - |
+| <xref:System.Diagnostics.ActivityContext.%23ctor(System.Diagnostics.ActivityTraceId,System.Diagnostics.ActivitySpanId,System.Diagnostics.ActivityTraceFlags,System.String,System.Boolean)> | `traceOptions` | `traceFlags` |
+| <xref:System.Globalization.CompareInfo.IsPrefix(System.ReadOnlySpan{System.Char},System.ReadOnlySpan{System.Char},System.Globalization.CompareOptions,System.Int32@)?displayProperty=nameWithType> | `suffix` | `prefix` |
+
+#### Reason for change
+
+The parameter names were changed for consistency and to avoid failures when using named arguments and reflection.
+
+#### Version introduced
+
+5.0 RC2
+
+#### Recommended action
+
+If you encounter a compiler error due to a parameter name change, update the parameter name accordingly.
+
+#### Category
+
+Core .NET libraries
+
+#### Affected APIs
+
+- <xref:System.Diagnostics.ActivityContext.%23ctor(System.Diagnostics.ActivityTraceId,System.Diagnostics.ActivitySpanId,System.Diagnostics.ActivityTraceFlags,System.String,System.Boolean)>
+- <xref:System.Globalization.CompareInfo.IsPrefix(System.ReadOnlySpan{System.Char},System.ReadOnlySpan{System.Char},System.Globalization.CompareOptions,System.Int32@)?displayProperty=fullName>
+
+<!--
+
+#### Affected APIs
+
+- `M:System.Diagnostics.ActivityContext.#ctor(System.Diagnostics.ActivityTraceId,System.Diagnostics.ActivitySpanId,System.Diagnostics.ActivityTraceFlags,System.String,System.Boolean)`
+- `M:System.Globalization.CompareInfo.IsPrefix(System.ReadOnlySpan{System.Char},System.ReadOnlySpan{System.Char},System.Globalization.CompareOptions,System.Int32@)`
+
+-->