diff --git a/ext/standard/string.c b/ext/standard/string.c
index b4398818ea3..e7102d0b03a 100644
--- a/ext/standard/string.c
+++ b/ext/standard/string.c
@@ -4555,8 +4555,8 @@ PHP_FUNCTION(addcslashes)
 		RETURN_STRINGL(str, str_len, 1);
 	}
 
-	RETURN_STRING(php_addcslashes(str, str_len, &Z_STRLEN_P(return_value), 0,
-								  what, what_len TSRMLS_CC), 0);
+	Z_STRVAL_P(return_value) = php_addcslashes(str, str_len, &Z_STRLEN_P(return_value), 0, what, what_len TSRMLS_CC);
+	RETURN_STRINGL(Z_STRVAL_P(return_value), Z_STRLEN_P(return_value), 0);
 }
 /* }}} */
 
diff --git a/ext/standard/tests/strings/bug40915.phpt b/ext/standard/tests/strings/bug40915.phpt
new file mode 100644
index 00000000000..854853ed2e3
Binary files /dev/null and b/ext/standard/tests/strings/bug40915.phpt differ