diff --git a/types/node/test/util.ts b/types/node/test/util.ts
index 3af024972e..14500161fd 100644
--- a/types/node/test/util.ts
+++ b/types/node/test/util.ts
@@ -89,14 +89,14 @@ import { readFile } from 'fs';
         }
 
         static test(): void {
-            const cfn = util.callbackify(this.fn);
-            const cfnE = util.callbackify(this.fnE);
-            const cfnT1 = util.callbackify(this.fnT1);
-            const cfnT1E = util.callbackify(this.fnT1E);
-            const cfnTResult = util.callbackify(this.fnTResult);
-            const cfnTResultE = util.callbackify(this.fnTResultE);
-            const cfnT1TResult = util.callbackify(this.fnT1TResult);
-            const cfnT1TResultE = util.callbackify(this.fnT1TResultE);
+            const cfn = util.callbackify(callbackifyTest.fn);
+            const cfnE = util.callbackify(callbackifyTest.fnE);
+            const cfnT1 = util.callbackify(callbackifyTest.fnT1);
+            const cfnT1E = util.callbackify(callbackifyTest.fnT1E);
+            const cfnTResult = util.callbackify(callbackifyTest.fnTResult);
+            const cfnTResultE = util.callbackify(callbackifyTest.fnTResultE);
+            const cfnT1TResult = util.callbackify(callbackifyTest.fnT1TResult);
+            const cfnT1TResultE = util.callbackify(callbackifyTest.fnT1TResultE);
 
             cfn((err: NodeJS.ErrnoException, ...args: string[]) => assert(err === null && args.length === 1 && args[0] === undefined));
             cfnE((err: NodeJS.ErrnoException, ...args: string[]) => assert(err.message === 'fail' && args.length === 0));
diff --git a/types/node/v10/node-tests.ts b/types/node/v10/node-tests.ts
index 6ae1c52bde..789b87b600 100644
--- a/types/node/v10/node-tests.ts
+++ b/types/node/v10/node-tests.ts
@@ -882,14 +882,14 @@ function bufferTests() {
             }
 
             static test(): void {
-                const cfn = util.callbackify(this.fn);
-                const cfnE = util.callbackify(this.fnE);
-                const cfnT1 = util.callbackify(this.fnT1);
-                const cfnT1E = util.callbackify(this.fnT1E);
-                const cfnTResult = util.callbackify(this.fnTResult);
-                const cfnTResultE = util.callbackify(this.fnTResultE);
-                const cfnT1TResult = util.callbackify(this.fnT1TResult);
-                const cfnT1TResultE = util.callbackify(this.fnT1TResultE);
+                const cfn = util.callbackify(callbackifyTest.fn);
+                const cfnE = util.callbackify(callbackifyTest.fnE);
+                const cfnT1 = util.callbackify(callbackifyTest.fnT1);
+                const cfnT1E = util.callbackify(callbackifyTest.fnT1E);
+                const cfnTResult = util.callbackify(callbackifyTest.fnTResult);
+                const cfnTResultE = util.callbackify(callbackifyTest.fnTResultE);
+                const cfnT1TResult = util.callbackify(callbackifyTest.fnT1TResult);
+                const cfnT1TResultE = util.callbackify(callbackifyTest.fnT1TResultE);
 
                 cfn((err: NodeJS.ErrnoException, ...args: string[]) => assert(err === null && args.length === 1 && args[0] === undefined));
                 cfnE((err: NodeJS.ErrnoException, ...args: string[]) => assert(err.message === 'fail' && args.length === 0));