diff --git a/codegen-core/common-test-models/rest-json-extras.smithy b/codegen-core/common-test-models/rest-json-extras.smithy
index 10224b0c7cf..70472b4ca97 100644
--- a/codegen-core/common-test-models/rest-json-extras.smithy
+++ b/codegen-core/common-test-models/rest-json-extras.smithy
@@ -80,12 +80,16 @@ service RestJsonExtras {
         appliesTo: "client",
     },
     {
-        documentation: "Upper case error modeled lower case",
+        documentation: """
+            Upper case error modeled lower case.
+            Servers render the full shape ID (including namespace), since some
+            existing clients rely on it to deserialize the error shape and fail
+            if only the shape name is present.""",
         id: "ServiceLevelErrorServer",
         protocol: "aws.protocols#restJson1",
         code: 500,
         body: "{}",
-        headers: { "X-Amzn-Errortype": "ExtraError" },
+        headers: { "X-Amzn-Errortype": "aws.protocoltests.restjson#ExtraError" },
         params: {},
         appliesTo: "server",
     }
diff --git a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/RestJson.kt b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/RestJson.kt
index 7a25fabfdb6..60029cdaf0e 100644
--- a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/RestJson.kt
+++ b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/RestJson.kt
@@ -81,9 +81,15 @@ open class RestJson(val codegenContext: CodegenContext) : Protocol {
     /**
      * RestJson1 implementations can denote errors in responses in several ways.
      * New server-side protocol implementations MUST use a header field named `X-Amzn-Errortype`.
+     *
+     * Note that the spec says that implementations SHOULD strip the error shape ID's namespace.
+     * However, our server implementation renders the full shape ID (including namespace), since some
+     * existing clients rely on it to deserialize the error shape and fail if only the shape name is present.
+     * This is compliant with the spec, see https://github.com/awslabs/smithy/pull/1493.
+     * See https://github.com/awslabs/smithy/issues/1494 too.
      */
     override fun additionalErrorResponseHeaders(errorShape: StructureShape): List<Pair<String, String>> =
-        listOf("x-amzn-errortype" to errorShape.id.name)
+        listOf("x-amzn-errortype" to errorShape.id.toString())
 
     override fun structuredDataParser(operationShape: OperationShape): StructuredDataParserGenerator =
         JsonParserGenerator(codegenContext, httpBindingResolver, ::restJsonFieldName)
diff --git a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/protocol/ServerProtocolTestGenerator.kt b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/protocol/ServerProtocolTestGenerator.kt
index 01120f4fc9b..a83a8a3c6fb 100644
--- a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/protocol/ServerProtocolTestGenerator.kt
+++ b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/protocol/ServerProtocolTestGenerator.kt
@@ -1194,6 +1194,13 @@ class ServerProtocolTestGenerator(
         ): HttpRequestTestCase =
             testCase.toBuilder().putHeader("x-amz-target", "JsonProtocol.${operationShape.id.name}").build()
 
+        private fun fixRestJsonInvalidGreetingError(testCase: HttpResponseTestCase): HttpResponseTestCase =
+            testCase.toBuilder().putHeader("X-Amzn-Errortype", "aws.protocoltests.restjson#InvalidGreeting").build()
+        private fun fixRestJsonEmptyComplexErrorWithNoMessage(testCase: HttpResponseTestCase): HttpResponseTestCase =
+            testCase.toBuilder().putHeader("X-Amzn-Errortype", "aws.protocoltests.restjson#ComplexError").build()
+        private fun fixRestJsonComplexErrorWithNoMessage(testCase: HttpResponseTestCase): HttpResponseTestCase =
+            testCase.toBuilder().putHeader("X-Amzn-Errortype", "aws.protocoltests.restjson#ComplexError").build()
+
         // These are tests whose definitions in the `awslabs/smithy` repository are wrong.
         // This is because they have not been written from a server perspective, and as such the expected `params` field is incomplete.
         // TODO(https://github.com/awslabs/smithy-rs/issues/1288): Contribute a PR to fix them upstream.
@@ -1270,6 +1277,11 @@ class ServerProtocolTestGenerator(
         )
 
         private val BrokenResponseTests: Map<Pair<String, String>, KFunction1<HttpResponseTestCase, HttpResponseTestCase>> =
-            mapOf()
+            // TODO(https://github.com/awslabs/smithy/issues/1494)
+            mapOf(
+                Pair(RestJson, "RestJsonInvalidGreetingError") to ::fixRestJsonInvalidGreetingError,
+                Pair(RestJson, "RestJsonEmptyComplexErrorWithNoMessage") to ::fixRestJsonEmptyComplexErrorWithNoMessage,
+                Pair(RestJson, "RestJsonComplexErrorWithNoMessage") to ::fixRestJsonComplexErrorWithNoMessage,
+            )
     }
 }
diff --git a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/protocols/ServerHttpBoundProtocolGenerator.kt b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/protocols/ServerHttpBoundProtocolGenerator.kt
index 2cf86be5eb1..d0ed29357c2 100644
--- a/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/protocols/ServerHttpBoundProtocolGenerator.kt
+++ b/codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/protocols/ServerHttpBoundProtocolGenerator.kt
@@ -32,6 +32,7 @@ import software.amazon.smithy.rust.codegen.core.rustlang.RustWriter
 import software.amazon.smithy.rust.codegen.core.rustlang.Writable
 import software.amazon.smithy.rust.codegen.core.rustlang.asType
 import software.amazon.smithy.rust.codegen.core.rustlang.conditionalBlock
+import software.amazon.smithy.rust.codegen.core.rustlang.escape
 import software.amazon.smithy.rust.codegen.core.rustlang.render
 import software.amazon.smithy.rust.codegen.core.rustlang.rust
 import software.amazon.smithy.rust.codegen.core.rustlang.rustBlock
@@ -635,7 +636,7 @@ private class ServerHttpBoundProtocolTraitImplGenerator(
                     builder = #{header_util}::set_response_header_if_absent(
                         builder,
                         http::header::HeaderName::from_static("$headerName"),
-                        "$headerValue"
+                        "${escape(headerValue)}"
                     );
                     """,
                     *codegenScope,