diff --git a/Makefile b/Makefile
index 76b8da4..f09742c 100644
--- a/Makefile
+++ b/Makefile
@@ -30,6 +30,8 @@ TEST := -v --run RegExp
 TEST := -v --run stringToFloat 
 TEST := -v --run TryFinally 
 TEST := -v --run RegExp_exec
+TEST := -v --run _panic
+TEST := -v --run TransformRegExp
 TEST := .
 
 test: test-i
diff --git a/otto_test.go b/otto_test.go
index f8a38e2..66233bb 100644
--- a/otto_test.go
+++ b/otto_test.go
@@ -58,6 +58,7 @@ func TestTransformRegExp(t *testing.T) {
 
 	Is(transformRegExp(`\\|'|\r|\n|\t|\u2028|\u2029`), `\\|'|\r|\n|\t|\x{2028}|\x{2029}`)
 	Is(transformRegExp(`\x`), `x`)
+	Is(transformRegExp(`\u0z01\x\undefined`), `u0z01xundefined`)
 }
 
 func TestIsValidRegExp(t *testing.T) {
diff --git a/panic_test.go b/panic_test.go
index fd03c21..0f4492c 100644
--- a/panic_test.go
+++ b/panic_test.go
@@ -23,7 +23,13 @@ func Test_panic(t *testing.T) {
 	// without panic
 	test(`
 		var abc = 0x0410;
-		var def = String.fromCharCode(abc)
-		new RegExp("\\c" + def).exec(def)
+		var def = String.fromCharCode(abc);
+		new RegExp("\\c" + def).exec(def);
 	`, "null")
+
+	// Test transforming a transformable regular expression without a panic
+	test(`
+		new RegExp("\\u0000");
+		new RegExp("\\undefined").test("undefined");
+	`, "true")
 }
diff --git a/type_regexp.go b/type_regexp.go
index cafd5c8..fc9dba1 100644
--- a/type_regexp.go
+++ b/type_regexp.go
@@ -128,9 +128,8 @@ func execResultToArray(runtime *_runtime, target string, result []int) *_object
 var transformRegExp_matchSlashU = regexp.MustCompile(`\\u([[:xdigit:]]{1,4})`)
 var transformRegExp_escape_c = regexp.MustCompile(`\\c([A-Za-z])`)
 var transformRegExp_unescape_c = regexp.MustCompile(`\\c`)
-var transformRegExp_unescape = regexp.MustCompile(strings.NewReplacer("\n", "", "\t", "", " ", "").Replace(`
-
-	(?:
+var transformRegExp_unescape = []*regexp.Regexp{
+	regexp.MustCompile(strings.NewReplacer("\n", "", "\t", "", " ", "").Replace(`
 		\\(
 		[
 			\x{0043}\x{0045}-\x{004F}
@@ -140,40 +139,24 @@ var transformRegExp_unescape = regexp.MustCompile(strings.NewReplacer("\n", "",
 			\x{0080}-\x{FFFF}
 		]
 		)()
-	) |
-	(?:
-		\\(u)([^[:xdigit:]])
-	) |
-	(?:
-		\\(u)([:xdigit:][^[:xdigit:]])
-	) |
-	(?:
-		\\(u)([:xdigit:][:xdigit:][^[:xdigit:]])
-	) |
-	(?:
-		\\(u)([:xdigit:][:xdigit:][:xdigit:][^[:xdigit:]])
-	) |
-	(?:
-		\\(x)([^[:xdigit:]])
-	) |
-	(?:
-		\\(x)([:xdigit:][^[:xdigit:]])
-	)
+	`)),
+	regexp.MustCompile(`\\(u)([^[:xdigit:]])`),
+	regexp.MustCompile(`\\(u)([[:xdigit:]][^[:xdigit:]])`),
+	regexp.MustCompile(`\\(u)([[:xdigit:]][[:xdigit:]][^[:xdigit:]])`),
+	regexp.MustCompile(`\\(u)([[:xdigit:]][[:xdigit:]][[:xdigit:]][^[:xdigit:]])`),
+	regexp.MustCompile(`\\(x)([^[:xdigit:]])`),
+	regexp.MustCompile(`\\(x)([[:xdigit:]][^[:xdigit:]])`),
+}
 
-`))
-var transformRegExp_unescapeDollar = regexp.MustCompile(strings.NewReplacer("\n", "", "\t", "", " ", "").Replace(`
-
-	(?:
-		\\([cux])$
-	)
-
-`))
+var transformRegExp_unescapeDollar = regexp.MustCompile(`\\([cux])$`)
 // TODO Go "regexp" bug? Can't do: (?:)|(?:$)
 
 func transformRegExp(ecmaRegExp string) (goRegExp string) {
 	// https://bugzilla.mozilla.org/show_bug.cgi/show_bug.cgi?id=334158
 	tmp := []byte(ecmaRegExp)
-	tmp = transformRegExp_unescape.ReplaceAll(tmp, []byte(`$1$2`))
+	for _, value := range transformRegExp_unescape {
+		tmp = value.ReplaceAll(tmp, []byte(`$1$2`))
+	}
 	tmp = transformRegExp_escape_c.ReplaceAllFunc(tmp, func(in []byte) []byte{
 		in = bytes.ToUpper(in)
 		return []byte(fmt.Sprintf("\\%o", in[0] - 64)) // \cA => \001 (A == 65)