fix compiler warnings
diff --git a/src/libFLAC/metadata_object.c b/src/libFLAC/metadata_object.c
index fdfc824..3cfe89c 100644
--- a/src/libFLAC/metadata_object.c
+++ b/src/libFLAC/metadata_object.c
@@ -1238,7 +1238,7 @@
 
 	{
 		int i;
-		unsigned field_name_length;
+		size_t field_name_length;
 		const FLAC__byte *eq = (FLAC__byte*)memchr(entry.entry, '=', entry.length);
 
 		FLAC__ASSERT(0 != eq);