diff -r 1478fc5cf632 src/lib/base64.c
--- a/src/lib/base64.c	Sun Oct 21 20:36:35 2007 +0300
+++ b/src/lib/base64.c	Mon Oct 22 10:11:40 2007 -0700
@@ -128,6 +128,8 @@ int base64_decode(const void *src, size_
 		buffer_append(dest, output, 3);
 	}
 
+	i_assert(src_pos <= src_size);
+
 	for (; src_pos < src_size; src_pos++) {
 		if (!IS_EMPTY(src_c[src_pos]))
 			break;
@@ -136,6 +138,7 @@ int base64_decode(const void *src, size_
 	if (src_pos_r != NULL)
 		*src_pos_r = src_pos;
 
+	i_assert(src_pos <= src_size);
 	return ret;
 }