Index: src/base64.m
==================================================================
--- src/base64.m
+++ src/base64.m
@@ -109,11 +109,11 @@
 
 	for (i = 0; i < length; i += 4) {
 		uint32_t sb = 0;
 		uint8_t count = 3;
 		char db[3];
-		char tmp;
+		int8_t tmp;
 
 		if (buffer[i] > 0x7F || buffer[i + 1] > 0x7F ||
 		    buffer[i + 2] > 0x7F || buffer[i + 3] > 0x7F)
 			return NO;