diff --git a/include/xo/tokenizer/input_state.hpp b/include/xo/tokenizer/input_state.hpp
index 0cea1155..fbff7e57 100644
--- a/include/xo/tokenizer/input_state.hpp
+++ b/include/xo/tokenizer/input_state.hpp
@@ -247,7 +247,7 @@ namespace xo {
         input_state<CharT>::advance_until(const CharT * pos) {
             scope log(XO_DEBUG(debug_flag_));
 
-            assert(current_line_.lo() <= pos && pos < current_line_.hi());
+            assert(current_line_.lo() <= pos && pos <= current_line_.hi());
 
             this->current_pos_ = pos - current_line_.lo();