diff --git a/build_tools/aws-sdk-code-generator/spec/protocols/output/rest-json.json b/build_tools/aws-sdk-code-generator/spec/protocols/output/rest-json.json
index f64ed4681f0..d85cf974ce5 100644
--- a/build_tools/aws-sdk-code-generator/spec/protocols/output/rest-json.json
+++ b/build_tools/aws-sdk-code-generator/spec/protocols/output/rest-json.json
@@ -1032,6 +1032,44 @@
           "headers": {},
           "body": "{\"UnionMember\": {\"SomeUnknownMember\": \"un-modeled member\"}}"
         }
+      },
+      {
+        "given": {
+          "output": {
+            "shape": "OutputShape"
+          },
+          "name": "OperationName"
+        },
+        "result": {
+          "UnionMember": {"S":  "string value"}
+        },
+        "resultClass": {
+          "UnionMember": "UnionType::S"
+        },
+        "response": {
+          "status_code": 200,
+          "headers": {},
+          "body": "{\"UnionMember\": {\"__type\": \"UnionType\", \"S\": \"string value\"}}"
+        }
+      },
+      {
+        "given": {
+          "output": {
+            "shape": "OutputShape"
+          },
+          "name": "OperationName"
+        },
+        "result": {
+          "UnionMember": {"Unknown":  {"name": "SomeUnknownMember", "value": "un-modeled member"}}
+        },
+        "resultClass": {
+          "UnionMember": "UnionType::Unknown"
+        },
+        "response": {
+          "status_code": 200,
+          "headers": {},
+          "body": "{\"UnionMember\": {\"SomeUnknownMember\": \"un-modeled member\", \"__type\": \"UnionType\"}}"
+        }
       }
     ]
   }
diff --git a/gems/aws-sdk-core/CHANGELOG.md b/gems/aws-sdk-core/CHANGELOG.md
index 6eb8ec46376..9814d7e416b 100644
--- a/gems/aws-sdk-core/CHANGELOG.md
+++ b/gems/aws-sdk-core/CHANGELOG.md
@@ -1,6 +1,8 @@
 Unreleased Changes
 ------------------
 
+* Issue - Ignore `__type` when deserializing Unions.
+
 3.185.0 (2023-10-02)
 ------------------
 
diff --git a/gems/aws-sdk-core/lib/aws-sdk-core/json/parser.rb b/gems/aws-sdk-core/lib/aws-sdk-core/json/parser.rb
index bd47974db52..00aed911932 100644
--- a/gems/aws-sdk-core/lib/aws-sdk-core/json/parser.rb
+++ b/gems/aws-sdk-core/lib/aws-sdk-core/json/parser.rb
@@ -28,7 +28,7 @@ def structure(ref, values, target = nil)
           member_name, member_ref = shape.member_by_location_name(key)
           if member_ref
             target[member_name] = parse_ref(member_ref, value)
-          elsif shape.union
+          elsif shape.union && key != '__type'
             target[:unknown] = { 'name' => key, 'value' => value }
           end
         end