diff --git a/src/jsutils/instanceOf.js b/src/jsutils/instanceOf.js
index 8c37778360..cf5e204a0a 100644
--- a/src/jsutils/instanceOf.js
+++ b/src/jsutils/instanceOf.js
@@ -16,16 +16,18 @@ declare function instanceOf(
   constructor: mixed,
 ): boolean %checks(value instanceof constructor);
 
-// eslint-disable-next-line no-redeclare
-export default function instanceOf(value, constructor) {
-  if (value instanceof constructor) {
-    return true;
-  }
-  if (value) {
-    const valueConstructor = value.constructor;
-    if (valueConstructor && valueConstructor.name === constructor.name) {
-      throw new Error(
-        `Cannot use ${constructor.name} "${value}" from another module or realm.
+export default (process && process.env.NODE_ENV !== 'production'
+  ? // eslint-disable-next-line no-shadow
+    function instanceOf(value: any, constructor: any) {
+      if (value instanceof constructor) {
+        return true;
+      }
+      if (value) {
+        const valueClass = value.constructor;
+        const className = constructor.name;
+        if (valueClass && valueClass.name === className) {
+          throw new Error(
+            `Cannot use ${className} "${value}" from another module or realm.
 
 Ensure that there is only one instance of "graphql" in the node_modules
 directory. If different versions of "graphql" are the dependencies of other
@@ -37,8 +39,12 @@ Duplicate "graphql" modules cannot be used at the same time since different
 versions may have different capabilities and behavior. The data from one
 version used in the function from another could produce confusing and
 spurious results.`,
-      );
+          );
+        }
+      }
+      return false;
     }
-  }
-  return false;
-}
+  : // eslint-disable-next-line no-shadow
+    function instanceOf(value: any, constructor: any) {
+      return value instanceof constructor;
+    });