diff --git a/src/Libraries/Microsoft.Extensions.AI/ChatCompletion/FunctionInvokingChatClient.cs b/src/Libraries/Microsoft.Extensions.AI/ChatCompletion/FunctionInvokingChatClient.cs
index cd449248867..2a760cb1d8b 100644
--- a/src/Libraries/Microsoft.Extensions.AI/ChatCompletion/FunctionInvokingChatClient.cs
+++ b/src/Libraries/Microsoft.Extensions.AI/ChatCompletion/FunctionInvokingChatClient.cs
@@ -1542,7 +1542,7 @@ private static bool CurrentActivityIsInvokeAgent
                 ref List<ApprovalResultWithRequestMessage>? targetList = ref approvalResponse.Approved ? ref approvedFunctionCalls : ref rejectedFunctionCalls;
 
                 ChatMessage? requestMessage = null;
-                _ = allApprovalRequestsMessages?.TryGetValue(approvalResponse.FunctionCall.CallId, out requestMessage);
+                _ = allApprovalRequestsMessages?.TryGetValue(approvalResponse.Id, out requestMessage);
 
                 (targetList ??= []).Add(new() { Response = approvalResponse, RequestMessage = requestMessage });
             }
diff --git a/test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/FunctionInvokingChatClientApprovalsTests.cs b/test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/FunctionInvokingChatClientApprovalsTests.cs
index dd77ef370c6..aa465054916 100644
--- a/test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/FunctionInvokingChatClientApprovalsTests.cs
+++ b/test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/FunctionInvokingChatClientApprovalsTests.cs
@@ -1156,6 +1156,55 @@ public async Task FunctionCallsWithInvocationRequiredFalseAreNotReplacedWithAppr
         Assert.Equal(0, functionInvokedCount);
     }
 
+    [Fact]
+    public async Task ApprovalResponsePreservesOriginalRequestMessageMetadata()
+    {
+        var options = new ChatOptions
+        {
+            Tools =
+            [
+                new ApprovalRequiredAIFunction(AIFunctionFactory.Create(() => "Result 1", "Func1")),
+            ]
+        };
+
+        const string OriginalMessageId = "original-message-id";
+
+        // Create input with approval request containing a known MessageId on the containing message
+        List<ChatMessage> input =
+        [
+            new ChatMessage(ChatRole.User, "hello"),
+            new ChatMessage(ChatRole.Assistant,
+            [
+                new FunctionApprovalRequestContent("approval-request-id", new FunctionCallContent("function-call-id", "Func1"))
+            ]) { MessageId = OriginalMessageId }, // This MessageId should be preserved
+            new ChatMessage(ChatRole.User,
+            [
+                new FunctionApprovalResponseContent("approval-request-id", true, new FunctionCallContent("function-call-id", "Func1"))
+            ]),
+        ];
+
+        List<ChatMessage> downstreamClientOutput =
+        [
+            new ChatMessage(ChatRole.Assistant, "world"),
+        ];
+
+        // The reconstructed function call message should preserve the original MessageId
+        List<ChatMessage> expectedOutput =
+        [
+            new ChatMessage(ChatRole.Assistant, [new FunctionCallContent("function-call-id", "Func1")]) { MessageId = OriginalMessageId },
+            new ChatMessage(ChatRole.Tool, [new FunctionResultContent("function-call-id", result: "Result 1")]),
+            new ChatMessage(ChatRole.Assistant, "world"),
+        ];
+
+        var actualOutput = await InvokeAndAssertAsync(options, input, downstreamClientOutput, expectedOutput);
+
+        // Verify that the reconstructed function call message has the original MessageId, not a synthetic one
+        Assert.Equal(OriginalMessageId, actualOutput[0].MessageId);
+
+        actualOutput = await InvokeAndAssertStreamingAsync(options, input, downstreamClientOutput, expectedOutput);
+        Assert.Equal(OriginalMessageId, actualOutput[0].MessageId);
+    }
+
     private static Task<List<ChatMessage>> InvokeAndAssertAsync(
         ChatOptions? options,
         List<ChatMessage> input,