diff --git a/vpi/sdf_lexor.lex b/vpi/sdf_lexor.lex
index f8a263ccf..c14b89cca 100644
--- a/vpi/sdf_lexor.lex
+++ b/vpi/sdf_lexor.lex
@@ -27,6 +27,7 @@
 # include  "sdf_parse_priv.h"
 # include  "sdf_parse.h"
 # include  <stdlib.h>
+# include  <string.h>
 # include  <strings.h>
 # include  <assert.h>