diff --git a/codegen-client/src/test/kotlin/software/amazon/smithy/rust/codegen/client/smithy/NamingObstacleCourseTest.kt b/codegen-client/src/test/kotlin/software/amazon/smithy/rust/codegen/client/smithy/NamingObstacleCourseTest.kt
index aba0edc1a57800e0c789a802f967f2e00a21ed7c..addc4d8f1e8eef353f39c5df8db95daac02b7c2d 100644
--- a/codegen-client/src/test/kotlin/software/amazon/smithy/rust/codegen/client/smithy/NamingObstacleCourseTest.kt
+++ b/codegen-client/src/test/kotlin/software/amazon/smithy/rust/codegen/client/smithy/NamingObstacleCourseTest.kt
@@ -6,7 +6,10 @@
 package software.amazon.smithy.rust.codegen.client.smithy
 
 import org.junit.jupiter.api.Test
+import software.amazon.smithy.aws.traits.protocols.RestJson1Trait
+import software.amazon.smithy.aws.traits.protocols.RestXmlTrait
 import software.amazon.smithy.rust.codegen.client.testutil.clientIntegrationTest
+import software.amazon.smithy.rust.codegen.core.testutil.NamingObstacleCourseTestModels.reusedInputOutputShapesModel
 import software.amazon.smithy.rust.codegen.core.testutil.NamingObstacleCourseTestModels.rustPreludeEnumVariantsModel
 import software.amazon.smithy.rust.codegen.core.testutil.NamingObstacleCourseTestModels.rustPreludeEnumsModel
 import software.amazon.smithy.rust.codegen.core.testutil.NamingObstacleCourseTestModels.rustPreludeOperationsModel
@@ -32,4 +35,14 @@ class NamingObstacleCourseTest {
     fun `test Rust prelude enum variant names compile`() {
         clientIntegrationTest(rustPreludeEnumVariantsModel()) { _, _ -> }
     }
+
+    @Test
+    fun `test reuse of input and output shapes json`() {
+        clientIntegrationTest(reusedInputOutputShapesModel(RestJson1Trait.builder().build()))
+    }
+
+    @Test
+    fun `test reuse of input and output shapes xml`() {
+        clientIntegrationTest(reusedInputOutputShapesModel(RestXmlTrait.builder().build()))
+    }
 }
diff --git a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/ProtocolFunctions.kt b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/ProtocolFunctions.kt
index 53bdfc009f18401a6040fedc07402061ade8a883..c468fdca0bcbbe6be1c350aa1e79e01afd40fa44 100644
--- a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/ProtocolFunctions.kt
+++ b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/ProtocolFunctions.kt
@@ -18,6 +18,10 @@ import software.amazon.smithy.rust.codegen.core.smithy.CodegenContext
 import software.amazon.smithy.rust.codegen.core.smithy.RuntimeType
 import software.amazon.smithy.rust.codegen.core.smithy.RustSymbolProvider
 import software.amazon.smithy.rust.codegen.core.smithy.contextName
+import software.amazon.smithy.rust.codegen.core.smithy.traits.SyntheticInputTrait
+import software.amazon.smithy.rust.codegen.core.smithy.traits.SyntheticOutputTrait
+import software.amazon.smithy.rust.codegen.core.util.hasTrait
+import software.amazon.smithy.rust.codegen.core.util.letIf
 import software.amazon.smithy.rust.codegen.core.util.toSnakeCase
 
 /**
@@ -139,10 +143,13 @@ internal fun RustSymbolProvider.shapeModuleName(serviceShape: ServiceShape?, sha
 
 /** Creates a unique name for a ser/de function. */
 fun RustSymbolProvider.shapeFunctionName(serviceShape: ServiceShape?, shape: Shape): String {
+    val extras = "".letIf(shape.hasTrait<SyntheticOutputTrait>()) {
+        it + "_output"
+    }.letIf(shape.hasTrait<SyntheticInputTrait>()) { it + "_input" }
     val containerName = when (shape) {
         is MemberShape -> model.expectShape(shape.container).contextName(serviceShape).toSnakeCase()
         else -> shape.contextName(serviceShape).toSnakeCase()
-    }
+    } + extras
     return when (shape) {
         is MemberShape -> shape.memberName.toSnakeCase()
         is DocumentShape -> "document"
diff --git a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/NamingObstacleCourseTestModels.kt b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/NamingObstacleCourseTestModels.kt
index c45a7d099255042b4c200c53e24d38c270fbf855..72979545b94087e2eaa2c5306b0c1c6aab02b689 100644
--- a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/NamingObstacleCourseTestModels.kt
+++ b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/testutil/NamingObstacleCourseTestModels.kt
@@ -6,6 +6,7 @@
 package software.amazon.smithy.rust.codegen.core.testutil
 
 import software.amazon.smithy.model.Model
+import software.amazon.smithy.model.traits.Trait
 import software.amazon.smithy.rust.codegen.core.smithy.RuntimeType.Companion.preludeScope
 
 object NamingObstacleCourseTestModels {
@@ -169,4 +170,61 @@ object NamingObstacleCourseTestModels {
             """,
         )
     }.toString().asSmithyModel()
+
+    /**
+     * This targets two bug classes:
+     * - operation inputs used as nested outputs
+     * - operation outputs used as nested outputs
+     */
+    fun reusedInputOutputShapesModel(protocol: Trait) = """
+        namespace test
+        use ${protocol.toShapeId()}
+        use aws.api#service
+        @${protocol.toShapeId().name}
+        @service(sdkId: "test")
+        service Service {
+            version: "2006-03-01",
+            operations: [GetThing, ReuseGetThingIO]
+        }
+
+        // re-use get thing output in a list & in an operation
+        @http(uri: "/SomeOperation2", method: "POST")
+        operation GetThing {
+            output: GetThingOutput
+            input: GetThingInput
+        }
+
+        // an operation that re-uses the input and output shapes from `GetThing` above. this has caused issues in the
+        // past with operation/input shape confusion during function signature generation
+        @http(uri: "/SomeOperation3", method: "POST")
+        operation ReuseGetThingIO {
+            input: GetThingNested
+            output: GetThingNested
+        }
+
+        structure GetThingOutput {
+            @required
+            meta: String
+        }
+
+        structure GetThingInput {
+            @required
+            meta: String
+        }
+
+        // nested structure which reuses input and output shapes internally
+        structure GetThingNested {
+            thingsOut: GetThingOutputList,
+            thingsIn: GetThingInputList,
+            thingOut: GetThingOutput,
+            thingIn: GetThingInput
+        }
+
+        list GetThingOutputList {
+            member: GetThingOutput
+        }
+        list GetThingInputList {
+            member: GetThingInput
+        }
+    """.asSmithyModel()
 }