diff --git a/src/bits.c b/src/bits.c
index 5855f5a..96c00d0 100644
--- a/src/bits.c
+++ b/src/bits.c
@@ -28,7 +28,7 @@ static int fwrite_all(const void* _buf, size_t sz, size_t num, FILE* out)
 {
 	register size_t w, done=0;
 	register const unsigned char* buf = _buf;
-	while( (w = fwrite(buf+done, sz, num-done, out)) > 0 && done < num) done+=w;
+	while( (w = fwrite(buf+(sz*done), sz, num-done, out)) > 0 && done < num) done+=w;
 	if (done!=num) return 0;
 	else return 1;
 }