diff --git a/builtin/checkout-index.c b/builtin/checkout-index.c
index b1feda7d5e..4ed6b23954 100644
--- a/builtin/checkout-index.c
+++ b/builtin/checkout-index.c
@@ -14,7 +14,7 @@
 static int line_termination = '\n';
 static int checkout_stage; /* default to checkout stage0 */
 static int to_tempfile;
-static char topath[4][PATH_MAX + 1];
+static char topath[4][TEMPORARY_FILENAME_LENGTH + 1];
 
 static struct checkout state;
 
diff --git a/cache.h b/cache.h
index 85b544f38d..3118b7fc99 100644
--- a/cache.h
+++ b/cache.h
@@ -975,6 +975,7 @@ struct checkout {
 		 refresh_cache:1;
 };
 
+#define TEMPORARY_FILENAME_LENGTH 25
 extern int checkout_entry(struct cache_entry *ce, const struct checkout *state, char *topath);
 
 struct cache_def {
diff --git a/entry.c b/entry.c
index fbb4863103..7b7aa8167a 100644
--- a/entry.c
+++ b/entry.c
@@ -234,6 +234,14 @@ static int check_path(const char *path, int len, struct stat *st, int skiplen)
 	return lstat(path, st);
 }
 
+/*
+ * Write the contents from ce out to the working tree.
+ *
+ * When topath[] is not NULL, instead of writing to the working tree
+ * file named by ce, a temporary file is created by this function and
+ * its name is returned in topath[], which must be able to hold at
+ * least TEMPORARY_FILENAME_LENGTH bytes long.
+ */
 int checkout_entry(struct cache_entry *ce,
 		   const struct checkout *state, char *topath)
 {