diff --git a/winsup/cygwin/libc/base64.c b/winsup/cygwin/libc/base64.c
index 933c92721..f6bdb872e 100644
--- a/winsup/cygwin/libc/base64.c
+++ b/winsup/cygwin/libc/base64.c
@@ -194,10 +194,7 @@ b64_ntop(u_char const *src, size_t srclength, char *target, size_t targsize) {
  */
 
 int
-b64_pton(src, target, targsize)
-	char const *src;
-	u_char *target;
-	size_t targsize;
+b64_pton(char const *src, unsigned char *target, size_t targsize)
 {
 	int tarindex, state, ch;
 	char *pos;