diff --git a/vpi/sdf_lexor.lex b/vpi/sdf_lexor.lex
index dcbd22021..c4b03d3fe 100644
--- a/vpi/sdf_lexor.lex
+++ b/vpi/sdf_lexor.lex
@@ -75,7 +75,7 @@ static int yywrap(void)
 
   /* Integer values */
 [0-9]+ {
-      yylval.int_val = strtoul(yytext, 0);
+      yylval.int_val = strtoul(yytext, 0, 10);
       return INTEGER;
 }