diff --git a/rhino/src/main/java/org/mozilla/javascript/ArrayLikeAbstractOperations.java b/rhino/src/main/java/org/mozilla/javascript/ArrayLikeAbstractOperations.java
index 5f6e416a5a..c35e29635c 100644
--- a/rhino/src/main/java/org/mozilla/javascript/ArrayLikeAbstractOperations.java
+++ b/rhino/src/main/java/org/mozilla/javascript/ArrayLikeAbstractOperations.java
@@ -6,7 +6,6 @@
 
 import java.io.Serializable;
 import java.util.Comparator;
-import org.mozilla.javascript.regexp.NativeRegExp;
 
 /** Contains implementation of shared methods useful for arrays and typed arrays. */
 public class ArrayLikeAbstractOperations {
@@ -146,20 +145,23 @@ static Function getCallbackArg(Context cx, Object callbackArg) {
         if (!(callbackArg instanceof Function)) {
             throw ScriptRuntime.notFunctionError(callbackArg);
         }
-        if (cx.getLanguageVersion() >= Context.VERSION_ES6
-                && (callbackArg instanceof NativeRegExp)) {
-            // Previously, it was allowed to pass RegExp instance as a callback (it implements
-            // Function)
-            // But according to ES2015 21.2.6 Properties of RegExp Instances:
-            // > RegExp instances are ordinary objects that inherit properties from the RegExp
-            // prototype object.
-            // > RegExp instances have internal slots [[RegExpMatcher]], [[OriginalSource]], and
-            // [[OriginalFlags]].
-            // so, no [[Call]] for RegExp-s
-            throw ScriptRuntime.notFunctionError(callbackArg);
-        }
 
         Function f = (Function) callbackArg;
+
+        if (cx.getLanguageVersion() >= Context.VERSION_ES6) {
+            RegExpProxy reProxy = ScriptRuntime.getRegExpProxy(cx);
+            if (reProxy != null && reProxy.isRegExp(f))
+                // Previously, it was allowed to pass RegExp instance as a callback (it implements
+                // Function)
+                // But according to ES2015 21.2.6 Properties of RegExp Instances:
+                // > RegExp instances are ordinary objects that inherit properties from the RegExp
+                // prototype object.
+                // > RegExp instances have internal slots [[RegExpMatcher]], [[OriginalSource]], and
+                // [[OriginalFlags]].
+                // so, no [[Call]] for RegExp-s
+                throw ScriptRuntime.notFunctionError(callbackArg);
+        }
+
         return f;
     }
 
diff --git a/rhino/src/main/java/org/mozilla/javascript/NativeString.java b/rhino/src/main/java/org/mozilla/javascript/NativeString.java
index 75c7e5b99e..75288c1379 100644
--- a/rhino/src/main/java/org/mozilla/javascript/NativeString.java
+++ b/rhino/src/main/java/org/mozilla/javascript/NativeString.java
@@ -13,7 +13,6 @@
 import java.text.Normalizer;
 import java.util.Locale;
 import org.mozilla.javascript.ScriptRuntime.StringIdOrIndex;
-import org.mozilla.javascript.regexp.NativeRegExp;
 
 /**
  * This class implements the String native object.
@@ -468,15 +467,20 @@ public Object execIdCall(
                 case Id_endsWith:
                     String thisString =
                             ScriptRuntime.toString(requireObjectCoercible(cx, thisObj, f));
-                    if (args.length > 0 && args[0] instanceof NativeRegExp) {
-                        if (ScriptableObject.isTrue(
-                                ScriptableObject.getProperty(
-                                        ScriptableObject.ensureScriptable(args[0]),
-                                        SymbolKey.MATCH))) {
-                            throw ScriptRuntime.typeErrorById(
-                                    "msg.first.arg.not.regexp",
-                                    String.class.getSimpleName(),
-                                    f.getFunctionName());
+
+                    if (args.length > 0) {
+                        RegExpProxy reProxy = ScriptRuntime.getRegExpProxy(cx);
+                        if (reProxy != null && args[0] instanceof Scriptable) {
+                            Scriptable arg0 = (Scriptable) args[0];
+                            if (reProxy.isRegExp(arg0)) {
+                                if (ScriptableObject.isTrue(
+                                        ScriptableObject.getProperty(arg0, SymbolKey.MATCH))) {
+                                    throw ScriptRuntime.typeErrorById(
+                                            "msg.first.arg.not.regexp",
+                                            String.class.getSimpleName(),
+                                            f.getFunctionName());
+                                }
+                            }
                         }
                     }
 
diff --git a/tests/build.gradle b/tests/build.gradle
index e015af1570..191d1cab53 100644
--- a/tests/build.gradle
+++ b/tests/build.gradle
@@ -10,6 +10,10 @@ dependencies {
     implementation project(':rhino')
     implementation project(':rhino-tools')
     implementation project(':rhino-xml')
+
+    testImplementation("com.tngtech.archunit:archunit-junit4:1.2.0") {
+        exclude group: 'junit'
+    }
 }
 
 test {
diff --git a/tests/src/test/java/org/mozilla/archunit/ArchitectureTest.java b/tests/src/test/java/org/mozilla/archunit/ArchitectureTest.java
new file mode 100644
index 0000000000..2826996e55
--- /dev/null
+++ b/tests/src/test/java/org/mozilla/archunit/ArchitectureTest.java
@@ -0,0 +1,40 @@
+/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.archunit;
+
+import static com.tngtech.archunit.lang.syntax.ArchRuleDefinition.noClasses;
+
+import com.tngtech.archunit.core.importer.ImportOption;
+import com.tngtech.archunit.junit.AnalyzeClasses;
+import com.tngtech.archunit.junit.ArchTest;
+import com.tngtech.archunit.junit.ArchUnitRunner;
+import com.tngtech.archunit.lang.ArchRule;
+import org.junit.runner.RunWith;
+
+/**
+ * Architecture tests.
+ *
+ * @author Ronald Brill
+ */
+@RunWith(ArchUnitRunner.class)
+@AnalyzeClasses(
+        packages = "org.mozilla.javascript",
+        importOptions = ImportOption.DoNotIncludeTests.class)
+public class ArchitectureTest {
+
+    /** Use only the RegExpProxy. */
+    @ArchTest
+    public static final ArchRule regExpProxyRule =
+            noClasses()
+                    .that()
+                    .resideOutsideOfPackage("org.mozilla.javascript.regexp..")
+                    .and()
+                    .doNotHaveFullyQualifiedName("org.mozilla.javascript.RegExpProxy")
+                    .should()
+                    .dependOnClassesThat()
+                    .resideInAnyPackage("org.mozilla.javascript.regexp..");
+}