diff --git a/codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/AwsEc2.java b/codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/AwsEc2.java
index 2dea7b7f1d35..f421e9f5305d 100644
--- a/codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/AwsEc2.java
+++ b/codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/AwsEc2.java
@@ -95,8 +95,8 @@ public void generateSharedComponents(GenerationContext context) {
             // Default a 404 status code to the NotFound code.
             writer.openBlock("if (output.statusCode == 404) {", "}", () -> writer.write("return 'NotFound';"));
 
-            // Default to an UnknownError code.
-            writer.write("return 'UnknownError';");
+            // Default to an empty error code so an unmodeled exception is built.
+            writer.write("return '';");
         });
         writer.write("");
     }
diff --git a/codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/AwsQuery.java b/codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/AwsQuery.java
index 99872f27e666..6e11f7f804bb 100644
--- a/codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/AwsQuery.java
+++ b/codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/AwsQuery.java
@@ -95,8 +95,8 @@ public void generateSharedComponents(GenerationContext context) {
             // Default a 404 status code to the NotFound code.
             writer.openBlock("if (output.statusCode == 404) {", "}", () -> writer.write("return 'NotFound';"));
 
-            // Default to an UnknownError code.
-            writer.write("return 'UnknownError';");
+            // Default to an empty error code so an unmodeled exception is built.
+            writer.write("return '';");
         });
         writer.write("");
     }
diff --git a/codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/AwsRestXml.java b/codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/AwsRestXml.java
index 4fe4db74f8ce..e5f2f2e59676 100644
--- a/codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/AwsRestXml.java
+++ b/codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/AwsRestXml.java
@@ -116,8 +116,8 @@ public void generateSharedComponents(GenerationContext context) {
             // Default a 404 status code to the NotFound code.
             writer.openBlock("if (output.statusCode == 404) {", "}", () -> writer.write("return 'NotFound';"));
 
-            // Default to an UnknownError code.
-            writer.write("return 'UnknownError';");
+            // Default to an empty error code so an unmodeled exception is built.
+            writer.write("return '';");
         });
         writer.write("");
     }