fix compiler warnings
diff --git a/src/libFLAC/metadata_iterators.c b/src/libFLAC/metadata_iterators.c
index 0ff0e00..33c5b25 100644
--- a/src/libFLAC/metadata_iterators.c
+++ b/src/libFLAC/metadata_iterators.c
@@ -2925,8 +2925,9 @@
 	FLAC__byte buffer[8192];
 	size_t n;
 
+	FLAC__ASSERT(bytes >= 0);
 	while(bytes > 0) {
-		n = min(sizeof(buffer), bytes);
+		n = min(sizeof(buffer), (size_t)bytes);
 		if(fread(buffer, 1, n, file) != n) {
 			*status = FLAC__METADATA_SIMPLE_ITERATOR_STATUS_READ_ERROR;
 			return false;
@@ -2946,8 +2947,9 @@
 	FLAC__byte buffer[8192];
 	size_t n;
 
+	FLAC__ASSERT(bytes >= 0);
 	while(bytes > 0) {
-		n = min(sizeof(buffer), bytes);
+		n = min(sizeof(buffer), (size_t)bytes);
 		if(read_cb(buffer, 1, n, handle) != n) {
 			*status = FLAC__METADATA_SIMPLE_ITERATOR_STATUS_READ_ERROR;
 			return false;