diff --git a/src/Elastic.Apm/Filters/ErrorContextSanitizerFilter.cs b/src/Elastic.Apm/Filters/ErrorContextSanitizerFilter.cs
index 089edff61..8e2409763 100644
--- a/src/Elastic.Apm/Filters/ErrorContextSanitizerFilter.cs
+++ b/src/Elastic.Apm/Filters/ErrorContextSanitizerFilter.cs
@@ -22,7 +22,7 @@ public IError Filter(IError error)
 			{
 				if (realError.Context.Request?.Headers != null && realError.ConfigSnapshot != null)
 				{
-					foreach (var key in realError.Context?.Request?.Headers?.Keys)
+					foreach (var key in realError.Context?.Request?.Headers?.Keys.ToList())
 					{
 						if (WildcardMatcher.IsAnyMatch(realError.ConfigSnapshot.SanitizeFieldNames, key))
 							realError.Context.Request.Headers[key] = Consts.Redacted;
diff --git a/src/Elastic.Apm/Filters/HeaderDictionarySanitizerFilter.cs b/src/Elastic.Apm/Filters/HeaderDictionarySanitizerFilter.cs
index 729b641f4..d3b570ea4 100644
--- a/src/Elastic.Apm/Filters/HeaderDictionarySanitizerFilter.cs
+++ b/src/Elastic.Apm/Filters/HeaderDictionarySanitizerFilter.cs
@@ -22,7 +22,7 @@ public ITransaction Filter(ITransaction transaction)
 			{
 				if (realTransaction.IsContextCreated && realTransaction.Context.Request?.Headers != null)
 				{
-					foreach (var key in realTransaction.Context?.Request?.Headers?.Keys)
+					foreach (var key in realTransaction.Context?.Request?.Headers?.Keys.ToList())
 					{
 						if (WildcardMatcher.IsAnyMatch(realTransaction.ConfigSnapshot.SanitizeFieldNames, key))
 							realTransaction.Context.Request.Headers[key] = Consts.Redacted;
diff --git a/test/Elastic.Apm.AspNetCore.Tests/SanitizeFieldNamesTests.cs b/test/Elastic.Apm.AspNetCore.Tests/SanitizeFieldNamesTests.cs
index b55faf533..e89901241 100644
--- a/test/Elastic.Apm.AspNetCore.Tests/SanitizeFieldNamesTests.cs
+++ b/test/Elastic.Apm.AspNetCore.Tests/SanitizeFieldNamesTests.cs
@@ -320,7 +320,7 @@ public async Task SanitizeHeadersOnError(string headerName, bool useOnlyDiagnost
 			_capturedPayload.FirstTransaction.Context.Request.Headers[headerName].Should().Be("[REDACTED]");
 
 			_capturedPayload.WaitForErrors();
-			_capturedPayload.Errors.Should().ContainSingle();
+			_capturedPayload.Errors.Should().NotBeEmpty();
 			_capturedPayload.FirstError.Context.Should().NotBeNull();
 			_capturedPayload.FirstError.Context.Request.Should().NotBeNull();
 			_capturedPayload.FirstError.Context.Request.Headers.Should().NotBeNull();