diff --git a/ext/session/session.c b/ext/session/session.c
index 0301108addd98..d263ac6d6e0bb 100644
--- a/ext/session/session.c
+++ b/ext/session/session.c
@@ -451,6 +451,11 @@ PS_SERIALIZER_ENCODE_FUNC(php)
 
 	PS_ENCODE_LOOP(
 			smart_str_appendl(&buf, key, (unsigned char) key_length);
+			if (memchr(key, PS_DELIMITER, key_length)) {
+				PHP_VAR_SERIALIZE_DESTROY(var_hash);
+				smart_str_free(&buf);				
+				return FAILURE;
+			}
 			smart_str_appendc(&buf, PS_DELIMITER);
 			
 			php_var_serialize(&buf, struc, &var_hash TSRMLS_CC);