diff --git a/ext/standard/crypt_freesec.c b/ext/standard/crypt_freesec.c
index bc74d1cb2c4..c30616eed72 100644
--- a/ext/standard/crypt_freesec.c
+++ b/ext/standard/crypt_freesec.c
@@ -172,7 +172,7 @@ static u_int32_t bits32[32] =
 
 static u_char	bits8[8] = { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
 
-static u_char	ascii64[] =
+static unsigned char	ascii64[] =
 	 "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
 /*	  0000000000111111111122222222223333333333444444444455555555556666 */
 /*	  0123456789012345678901234567890123456789012345678901234567890123 */