diff --git a/library/base64.c b/library/base64.c
index 327c022..6a6c3ae 100644
--- a/library/base64.c
+++ b/library/base64.c
@@ -59,7 +59,7 @@
  * Encode a buffer into base64 format
  */
 int base64_encode( unsigned char *dst, int *dlen,
-                   unsigned char *src, int  slen )
+                   const unsigned char *src, int  slen )
 {
     int i, n;
     int C1, C2, C3;
@@ -122,7 +122,7 @@
  * Decode a base64-formatted buffer
  */
 int base64_decode( unsigned char *dst, int *dlen,
-                   unsigned char *src, int  slen )
+                   const unsigned char *src, int  slen )
 {
     int i, j, n;
     unsigned long x;