diff --git a/TODO.TXT b/TODO.TXT
index ed861b3..976313c 100644
--- a/TODO.TXT
+++ b/TODO.TXT
@@ -1,4 +1,4 @@
-  resolve all TODO in source codes
+X resolve all TODO in source codes
   remove f16/f32/f64 types
   partial code generation for C (divide decls and functions)
   release v1.0.1
diff --git a/biner.l b/biner.l
index c98bf4b..a58ce7c 100644
--- a/biner.l
+++ b/biner.l
@@ -20,11 +20,18 @@ D [0-9]
 I [A-Za-z_]
 H [0-9A-Fa-f]
 
+%x IN_COMMENT
+
 %%
 
 [ \t\r\n]+ count_();
 "//".*     count_();
-[/][*][^*]*[*]+([^*/][^*]*[*]+)*[/] count_(); /* TODO: detect unterminated comment */
+
+<INITIAL>"/*"        { count_(); BEGIN(IN_COMMENT); }
+<IN_COMMENT>"*/"     { count_(); BEGIN(INITIAL); }
+<IN_COMMENT>[^\*\n]+ count_();
+<IN_COMMENT>"*"      count_();
+<IN_COMMENT>"\n"     count_();
 
 "==" { count_(); return EQUAL; }
 "!=" { count_(); return NEQUAL; }