diff --git a/src/jsutils/instanceOf.js b/src/jsutils/instanceOf.js
index e55cd13f73..2d0bf48208 100644
--- a/src/jsutils/instanceOf.js
+++ b/src/jsutils/instanceOf.js
@@ -1,3 +1,5 @@
+import { SYMBOL_TO_STRING_TAG } from '../polyfills/symbols';
+
 /**
  * A replacement for instanceof which includes an error warning when multi-realm
  * constructors are detected.
@@ -21,9 +23,23 @@ export default process.env.NODE_ENV === 'production'
         return true;
       }
       if (value) {
-        const valueClass = value.constructor;
-        const className = constructor.name;
-        if (className && valueClass && valueClass.name === className) {
+        const classTag = constructor?.prototype?.[SYMBOL_TO_STRING_TAG];
+        const className = classTag || constructor.name;
+        // When the constructor class defines a Symbol.toStringTag
+        // property, as most classes exported by graphql-js do, use it
+        // instead of constructor.name and value.constructor.name to
+        // detect module/realm duplication, since the Symbol.toStringTag
+        // string is immune to minification. This code runs only when
+        // process.env.NODE_ENV !== 'production', but minification is
+        // often enabled in non-production environments like 'staging'.
+        // In these environments, this error can be thrown mistakenly if
+        // we rely on constructor.name and value.constructor.name, since
+        // they could be minified to the same short string, even though
+        // value is legitimately _not_ instanceof constructor.
+        const valueName = classTag
+          ? value[SYMBOL_TO_STRING_TAG]
+          : value.constructor?.name;
+        if (typeof className === 'string' && valueName === className) {
           throw new Error(
             `Cannot use ${className} "${value}" from another module or realm.