diff --git a/usr.bin/m4/misc.c b/usr.bin/m4/misc.c
index d641ec56afe..1870323ccb3 100644
--- a/usr.bin/m4/misc.c
+++ b/usr.bin/m4/misc.c
@@ -121,7 +121,7 @@ void
 pbnumbase(int n, int base, int d)
 {
 	static char digits[36] = "0123456789abcdefghijklmnopqrstuvwxyz";
-	int num;
+	unsigned int num;
 	int printed = 0;
 
 	if (base > 36)