diff --git a/Tools/LambdaTestTool-v2/tests/Amazon.Lambda.TestTool.IntegrationTests/Helpers/ApiGatewayTestHelper.cs b/Tools/LambdaTestTool-v2/tests/Amazon.Lambda.TestTool.IntegrationTests/Helpers/ApiGatewayTestHelper.cs
index 67eed78c8..24f736961 100644
--- a/Tools/LambdaTestTool-v2/tests/Amazon.Lambda.TestTool.IntegrationTests/Helpers/ApiGatewayTestHelper.cs
+++ b/Tools/LambdaTestTool-v2/tests/Amazon.Lambda.TestTool.IntegrationTests/Helpers/ApiGatewayTestHelper.cs
@@ -65,7 +65,7 @@ public async Task AssertResponsesEqual(HttpResponseMessage actualResponse, HttpR
                 if (headersToIgnore.Contains(header.Key)) continue;
                 Assert.True(actualResponse.Headers.TryGetValues(header.Key, out var actualValues) ||
                             actualResponse.Content.Headers.TryGetValues(header.Key, out actualValues),
-                            $"Header '{header.Key}={string.Join(", ", header.Value)}' not found in actual response");
+                            $"Header '{header.Key}={string.Join(", ", header.Value.ToArray())}' not found in actual response");
 
                 var sortedExpectedValues = header.Value.OrderBy(v => v).ToArray();
                 var sortedActualValues = actualValues.OrderBy(v => v).ToArray();