diff --git a/docs/core/compatibility/6.0.md b/docs/core/compatibility/6.0.md
index 1fc65ecc5c091..2cea9d2590977 100644
--- a/docs/core/compatibility/6.0.md
+++ b/docs/core/compatibility/6.0.md
@@ -131,6 +131,7 @@ If you're migrating an app to .NET 6, the breaking changes listed here might aff
 | [IAsyncEnumerable serialization](serialization/6.0/iasyncenumerable-serialization.md) | ✔️ | ❌ | Preview 4 |
 | [JSON source-generation API refactoring](serialization/6.0/json-source-gen-api-refactor.md) | ❌ | ✔️ | RC 2 |
 | [JsonNode no longer supports C# `dynamic` type](serialization/6.0/jsonnode-dynamic-type.md) | ❌ | ✔️ | Preview 7 |
+| [JsonNumberHandlingAttribute on collection properties](serialization/6.0/jsonnumberhandlingattribute-behavior.md) | ❌ | ✔️ | RC 1 |
 | [New JsonSerializer source generator overloads](serialization/6.0/jsonserializer-source-generator-overloads.md) | ❌ | ✔️ | Preview 6 |
 
 ## Windows Forms
diff --git a/docs/core/compatibility/serialization/6.0/jsonnumberhandlingattribute-behavior.md b/docs/core/compatibility/serialization/6.0/jsonnumberhandlingattribute-behavior.md
new file mode 100644
index 0000000000000..9b0fd23ebe25e
--- /dev/null
+++ b/docs/core/compatibility/serialization/6.0/jsonnumberhandlingattribute-behavior.md
@@ -0,0 +1,46 @@
+---
+title: "Breaking change: JsonNumberHandlingAttribute on non-number collection properties"
+description: Learn about the .NET 6 breaking change where JsonNumberHandlingAttribute can now only be applied to properties that are collections of numbers.
+ms.date: 11/05/2021
+---
+# JsonNumberHandlingAttribute on collection properties
+
+A minor breaking change was introduced in .NET 6 with regard to the <xref:System.Text.Json.Serialization.JsonNumberHandlingAttribute> attribute. If you apply the attribute to a property that's a collection of non-number values and attempt to serialize or deserialize the property, an <xref:System.InvalidOperationException> is thrown. The attribute is only valid for properties that are collections of number types, for example:
+
+```csharp
+[JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
+public List<int> MyList { get; set; }
+```
+
+## Previous behavior
+
+Although it was ignored during serialization, <xref:System.Text.Json.Serialization.JsonNumberHandlingAttribute> could be applied to properties that were collections of non-number types. For example:
+
+```csharp
+[JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
+public List<MyClass> MyList { get; set; }
+```
+
+## New behavior
+
+Starting in .NET 6, if you apply <xref:System.Text.Json.Serialization.JsonNumberHandlingAttribute> to a property that's a collection of non-number values and attempt to serialize or deserialize the property, an <xref:System.InvalidOperationException> is thrown.
+
+## Version introduced
+
+6.0 Preview 1
+
+## Type of breaking change
+
+This change can affect [binary compatibility](../../categories.md#binary-compatibility).
+
+## Reason for change
+
+This change was a side effect of a performance optimization for the number handling feature.
+
+## Recommended action
+
+Remove the <xref:System.Text.Json.Serialization.JsonNumberHandlingAttribute> attribute from incompatible collection properties.
+
+## Affected APIs
+
+All of the <xref:System.Text.Json.JsonSerializer?displayProperty=fullName> serialization and deserialization methods.
diff --git a/docs/core/compatibility/toc.yml b/docs/core/compatibility/toc.yml
index 31473d2ee800a..6687cba3b3c6a 100644
--- a/docs/core/compatibility/toc.yml
+++ b/docs/core/compatibility/toc.yml
@@ -177,6 +177,8 @@ items:
           href: serialization/6.0/json-source-gen-api-refactor.md
         - name: JsonNode no longer supports C# `dynamic`
           href: serialization/6.0/jsonnode-dynamic-type.md
+        - name: JsonNumberHandlingAttribute on collection properties
+          href: serialization/6.0/jsonnumberhandlingattribute-behavior.md
         - name: New JsonSerializer source generator overloads
           href: serialization/6.0/jsonserializer-source-generator-overloads.md
       - name: Windows Forms
@@ -883,6 +885,8 @@ items:
           href: serialization/6.0/json-source-gen-api-refactor.md
         - name: JsonNode no longer supports C# `dynamic`
           href: serialization/6.0/jsonnode-dynamic-type.md
+        - name: JsonNumberHandlingAttribute on collection properties
+          href: serialization/6.0/jsonnumberhandlingattribute-behavior.md
         - name: New JsonSerializer source generator overloads
           href: serialization/6.0/jsonserializer-source-generator-overloads.md
       - name: .NET 5