diff --git a/package.json b/package.json
index 0de67ae2..a3a18e9f 100644
--- a/package.json
+++ b/package.json
@@ -88,7 +88,7 @@
     "mocha": "^2.3.4",
     "tsd": "^0.6.5",
     "tslint": "3.1.0-dev.1",
-    "typescript": "1.8.0-dev.20151128",
+    "typescript": "1.8.0-dev.20151201",
     "vinyl-source-stream": "^1.1.0"
   }
 }
diff --git a/tsconfig.json b/tsconfig.json
index 1e7c223f..b09d183c 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -5,7 +5,7 @@
         "module": "es2015",
         "moduleResolution": "node",
         "noImplicitAny": true,
-        "noImplicitReturns": false, // FIXME: #503 we'd like to enable this option again.
+        "noImplicitReturns": true,
         "outDir": "./dist/client/__obj/",
         "pretty": true,
         "preserveConstEnums": true,