diff --git a/merge-recursive.c b/merge-recursive.c
index 6b812d67e3..1d960fa64b 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1043,7 +1043,7 @@ static int merge_3way(struct merge_options *opt,
 		}
 	}
 
-	assert(a->path && b->path);
+	assert(a->path && b->path && o->path);
 	if (strcmp(a->path, b->path) ||
 	    (opt->ancestor != NULL && strcmp(a->path, o->path) != 0)) {
 		base_name = opt->ancestor == NULL ? NULL :