diff --git a/Zend/tests/readonly_function.phpt b/Zend/tests/readonly_function.phpt
new file mode 100644
index 0000000000000..0262b3b7348ce
--- /dev/null
+++ b/Zend/tests/readonly_function.phpt
@@ -0,0 +1,16 @@
+--TEST--
+Can use readonly as a function name
+--FILE--
+<?php
+
+function readonly() {
+    echo "Hi!\n";
+}
+
+readonly();
+readonly ();
+
+?>
+--EXPECT--
+Hi!
+Hi!
diff --git a/Zend/zend_language_scanner.l b/Zend/zend_language_scanner.l
index cc424bbec0a64..56c57a5a08543 100644
--- a/Zend/zend_language_scanner.l
+++ b/Zend/zend_language_scanner.l
@@ -1718,6 +1718,12 @@ NEWLINE ("\r"|"\n"|"\r\n")
 	RETURN_TOKEN_WITH_IDENT(T_READONLY);
 }
 
+/* Don't treat "readonly(" as a keyword, to allow using it as a function name. */
+<ST_IN_SCRIPTING>"readonly"[ \n\r\t]*"(" {
+	yyless(strlen("readonly"));
+	RETURN_TOKEN_WITH_STR(T_STRING, 0);
+}
+
 <ST_IN_SCRIPTING>"unset" {
 	RETURN_TOKEN_WITH_IDENT(T_UNSET);
 }