diff --git a/builtin/merge-file.c b/builtin/merge-file.c
index 232b768..04ae36a 100644
--- a/builtin/merge-file.c
+++ b/builtin/merge-file.c
@@ -75,7 +75,8 @@
 			names[i] = argv[i];
 		if (read_mmfile(mmfs + i, fname))
 			return -1;
-		if (buffer_is_binary(mmfs[i].ptr, mmfs[i].size))
+		if (mmfs[i].size > MAX_XDIFF_SIZE ||
+		    buffer_is_binary(mmfs[i].ptr, mmfs[i].size))
 			return error("Cannot merge binary files: %s",
 					argv[i]);
 	}