diff --git a/builtin_regexp.go b/builtin_regexp.go
index 88f0322..470b519 100644
--- a/builtin_regexp.go
+++ b/builtin_regexp.go
@@ -18,7 +18,10 @@ func builtinRegExp(call FunctionCall) Value {
 }
 
 func builtinNewRegExp(self *_object, _ Value, argumentList []Value) Value {
-	return toValue(self.runtime.newRegExp(valueOfArrayIndex(argumentList, 0), valueOfArrayIndex(argumentList, 1)))
+	return toValue(self.runtime.newRegExp(
+		valueOfArrayIndex(argumentList, 0),
+		valueOfArrayIndex(argumentList, 1),
+	))
 }
 
 func builtinRegExp_toString(call FunctionCall) Value {
diff --git a/global.go b/global.go
index 7b65c96..582302a 100644
--- a/global.go
+++ b/global.go
@@ -774,6 +774,12 @@ func (runtime *_runtime) newNumber(value Value) *_object {
 }
 
 func (runtime *_runtime) newRegExp(patternValue Value, flagsValue Value) *_object {
+	if object := patternValue._object(); object != nil {
+		if object.class == "RegExp" && flagsValue.IsDefined() {
+			panic(newTypeError("Cannot supply flags when constructing one RegExp from another"))
+		}
+	}
+
 	pattern := ""
 	if patternValue.IsDefined() {
 		pattern = toString(patternValue)
@@ -782,6 +788,7 @@ func (runtime *_runtime) newRegExp(patternValue Value, flagsValue Value) *_objec
 	if flagsValue.IsDefined() {
 		flags = toString(flagsValue)
 	}
+
 	return runtime._newRegExp(pattern, flags)
 }
 
diff --git a/regexp_test.go b/regexp_test.go
index 46e05a7..cf57d95 100644
--- a/regexp_test.go
+++ b/regexp_test.go
@@ -131,6 +131,10 @@ func TestRegExpCopying(t *testing.T) {
         abc.indicator = 1;
         [ abc.indicator, def.indicator ];
     `, "1,1")
+
+	test(`raise:
+        RegExp(new RegExp("\d"), "1");
+    `, "TypeError: Cannot supply flags when constructing one RegExp from another")
 }
 
 func TestRegExp_multiline(t *testing.T) {