diff --git a/src/libjsparser/lexer.c b/src/libjsparser/lexer.c
index 8419bc210..91e3985d9 100644
--- a/src/libjsparser/lexer.c
+++ b/src/libjsparser/lexer.c
@@ -56,7 +56,7 @@ static const char *token_start;
 static char
 get_char (size_t i)
 {
-  JERRY_ASSERT (i < buffer_size);
+  JERRY_ASSERT ((buffer + i) < (buffer_start + buffer_size));
   return *(buffer + i);
 }
 
@@ -950,4 +950,6 @@ void
 lexer_free (void)
 {
   mem_heap_free_block ((uint8_t *) strings_cache);
+  strings_cache = NULL;
+  strings_cache_size = 0;
 }
diff --git a/src/main.c b/src/main.c
index 5ce0a4f8a..7c8eeefae 100644
--- a/src/main.c
+++ b/src/main.c
@@ -52,11 +52,11 @@ parser_run (const char *script_source, size_t script_source_size, bool is_show_o
   offset = serializer_dump_strings (strings, strings_num);
   serializer_dump_nums (nums, nums_count, offset, strings_num);
   
-  lexer_free ();
-
   parser_init ();
   parser_parse_program ();
 
+  lexer_free ();
+
   opcodes = deserialize_bytecode ();
 
   optimizer_run_passes ((OPCODE *) opcodes);