diff --git a/src/libsodium/sodium/codecs.c b/src/libsodium/sodium/codecs.c
index 7e203a5c..247c9c0d 100644
--- a/src/libsodium/sodium/codecs.c
+++ b/src/libsodium/sodium/codecs.c
@@ -215,7 +215,9 @@ sodium_bin2base64(char * const b64, const size_t b64_maxlen,
     while (b64_pos < b64_len) {
         b64[b64_pos++] = '=';
     }
-    b64[b64_pos++] = 0;
+    do {
+        b64[b64_pos++] = 0U;
+    } while (b64_pos < b64_maxlen);
 
     return b64;
 }
diff --git a/test/default/sodium_utils.c b/test/default/sodium_utils.c
index d748f1ef..0da2ec34 100644
--- a/test/default/sodium_utils.c
+++ b/test/default/sodium_utils.c
@@ -161,7 +161,7 @@ main(void)
         b64_ = (char *) sodium_malloc(b64_len);
         randombytes_buf(bin, bin_len);
         memcpy(buf1, bin, bin_len);
-        b64 = sodium_bin2base64(b64_, b64_len + 10, bin, bin_len,
+        b64 = sodium_bin2base64(b64_, b64_len, bin, bin_len,
                                 sodium_base64_VARIANT_URLSAFE);
         assert(b64 != NULL);
         assert(sodium_base642bin(bin, bin_len + 10, b64, b64_len,