diff --git a/types/codemirror/test/index.ts b/types/codemirror/test/index.ts
index 39c601f159..9b9231b25c 100644
--- a/types/codemirror/test/index.ts
+++ b/types/codemirror/test/index.ts
@@ -13,9 +13,9 @@ var head = range.head;
 var from = range.from();
 var to = range.to();
 
-var myTextArea: HTMLTextAreaElement;
+var myTextArea: HTMLTextAreaElement = undefined!;
 var myCodeMirror3: CodeMirror.Editor = CodeMirror(function (elt) {
-    myTextArea.parentNode.replaceChild(elt, myTextArea);
+    myTextArea.parentNode!.replaceChild(elt, myTextArea);
 }, { value: myTextArea.value });
 
 var myCodeMirror4: CodeMirror.Editor = CodeMirror.fromTextArea(myTextArea);
diff --git a/types/codemirror/tsconfig.json b/types/codemirror/tsconfig.json
index 2ff349d98e..a2c6a52430 100644
--- a/types/codemirror/tsconfig.json
+++ b/types/codemirror/tsconfig.json
@@ -7,7 +7,7 @@
         ],
         "noImplicitAny": true,
         "noImplicitThis": true,
-        "strictNullChecks": false,
+        "strictNullChecks": true,
         "strictFunctionTypes": true,
         "baseUrl": "../",
         "typeRoots": [