diff --git a/sha1_file.c b/sha1_file.c
index c63264198ea3b52c78387e2f949b3cac7a7a256f..5475d781d4961e24e0b3165c45c337cbaf2a3557 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -442,6 +442,7 @@ void prepare_alt_odb(void)
 	read_info_alternates(get_object_directory(), 0);
 }
 
+/* Returns 1 if we have successfully freshened the file, 0 otherwise. */
 static int freshen_file(const char *fn)
 {
 	struct utimbuf t;
@@ -449,11 +450,18 @@ static int freshen_file(const char *fn)
 	return !utime(fn, &t);
 }
 
+/*
+ * All of the check_and_freshen functions return 1 if the file exists and was
+ * freshened (if freshening was requested), 0 otherwise. If they return
+ * 0, you should not assume that it is safe to skip a write of the object (it
+ * either does not exist on disk, or has a stale mtime and may be subject to
+ * pruning).
+ */
 static int check_and_freshen_file(const char *fn, int freshen)
 {
 	if (access(fn, F_OK))
 		return 0;
-	if (freshen && freshen_file(fn))
+	if (freshen && !freshen_file(fn))
 		return 0;
 	return 1;
 }