diff --git a/C_C++/flex/reject.l b/C_C++/flex/reject.l
new file mode 100644
index 0000000..3ffe612
--- /dev/null
+++ b/C_C++/flex/reject.l
@@ -0,0 +1,13 @@
+/* @BAKE
+    flex $@
+    gcc lex.yy.c -lfl
+    ./a.out
+   @STOP
+*/
+%option reject
+%%
+a        |
+ab       |
+abc      |
+abcd     REJECT; ECHO; 
+.|\n     /* eat up any unmatched character */