diff --git a/loadzip.cpp b/loadzip.cpp
index b59f8f7b..2e57179b 100644
--- a/loadzip.cpp
+++ b/loadzip.cpp
@@ -257,7 +257,8 @@ bool8 LoadZip (const char *zipname, uint32 *TotalFileSize, uint8 *buffer)
 	if (!(port == UNZ_END_OF_LIST_OF_FILE || port == UNZ_OK) || filesize == 0 ||
 		(len > 5 && strcasecmp(zipname + len - 5, ".msu1") == 0 && strcasecmp(filename, "program.rom") != 0))
 	{
-		assert(unzClose(file) == UNZ_OK);
+		if (unzClose(file) != UNZ_OK)
+			assert(FALSE);
 		return (FALSE);
 	}