diff --git a/smithy-model/src/test/resources/software/amazon/smithy/model/loader/valid/inline-io/inline-io.json b/smithy-model/src/test/resources/software/amazon/smithy/model/loader/valid/inline-io/inline-io.json
index d9e10708d34..76354f99a1a 100644
--- a/smithy-model/src/test/resources/software/amazon/smithy/model/loader/valid/inline-io/inline-io.json
+++ b/smithy-model/src/test/resources/software/amazon/smithy/model/loader/valid/inline-io/inline-io.json
@@ -203,6 +203,29 @@
                 "smithy.api#documentation": "Here too",
                 "smithy.api#output": {}
             }
+        },
+        "com.example#DuplicateTrait": {
+            "type": "operation",
+            "input": {
+                "target": "com.example#DuplicateTraitInput"
+            },
+            "output": {
+                "target": "com.example#DuplicateTraitOutput"
+            }
+        },
+        "com.example#DuplicateTraitInput": {
+            "type": "structure",
+            "members": {},
+            "traits": {
+                "smithy.api#input": {}
+            }
+        },
+        "com.example#DuplicateTraitOutput": {
+            "type": "structure",
+            "members": {},
+            "traits": {
+                "smithy.api#output": {}
+            }
         }
     }
 }
diff --git a/smithy-model/src/test/resources/software/amazon/smithy/model/loader/valid/inline-io/inline-io.smithy b/smithy-model/src/test/resources/software/amazon/smithy/model/loader/valid/inline-io/inline-io.smithy
index 6824166c4d8..2438c748680 100644
--- a/smithy-model/src/test/resources/software/amazon/smithy/model/loader/valid/inline-io/inline-io.smithy
+++ b/smithy-model/src/test/resources/software/amazon/smithy/model/loader/valid/inline-io/inline-io.smithy
@@ -67,3 +67,8 @@ operation HasDocComments {
         /// Here too
         {}
 }
+
+operation DuplicateTrait {
+    input := @input {}
+    output := @output {}
+}