diff --git a/builtin/am.c b/builtin/am.c
index 1aea657a7f..92e0e70069 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -1071,19 +1071,6 @@ static const char *msgnum(const struct am_state *state)
 	return sb.buf;
 }
 
-/**
- * Refresh and write index.
- */
-static void refresh_and_write_cache(void)
-{
-	struct lock_file lock_file = LOCK_INIT;
-
-	hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
-	refresh_cache(REFRESH_QUIET);
-	if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
-		die(_("unable to write index file"));
-}
-
 /**
  * Dies with a user-friendly message on how to proceed after resolving the
  * problem. This message can be overridden with state->resolvemsg.
@@ -1703,7 +1690,8 @@ static void am_run(struct am_state *state, int resume)
 
 	unlink(am_path(state, "dirtyindex"));
 
-	refresh_and_write_cache();
+	if (refresh_and_write_cache(REFRESH_QUIET, 0, 0) < 0)
+		die(_("unable to write index file"));
 
 	if (repo_index_has_changes(the_repository, NULL, &sb)) {
 		write_state_bool(state, "dirtyindex", 1);
diff --git a/cache.h b/cache.h
index b1da1ab08f..68a54f50ac 100644
--- a/cache.h
+++ b/cache.h
@@ -414,6 +414,7 @@ extern struct index_state the_index;
 #define add_file_to_cache(path, flags) add_file_to_index(&the_index, (path), (flags))
 #define chmod_cache_entry(ce, flip) chmod_index_entry(&the_index, (ce), (flip))
 #define refresh_cache(flags) refresh_index(&the_index, (flags), NULL, NULL, NULL)
+#define refresh_and_write_cache(refresh_flags, write_flags, gentle) repo_refresh_and_write_index(the_repository, (refresh_flags), (write_flags), (gentle), NULL, NULL, NULL)
 #define ce_match_stat(ce, st, options) ie_match_stat(&the_index, (ce), (st), (options))
 #define ce_modified(ce, st, options) ie_modified(&the_index, (ce), (st), (options))
 #define cache_dir_exists(name, namelen) index_dir_exists(&the_index, (name), (namelen))
@@ -812,6 +813,23 @@ void fill_stat_cache_info(struct index_state *istate, struct cache_entry *ce, st
 #define REFRESH_IN_PORCELAIN	0x0020	/* user friendly output, not "needs update" */
 #define REFRESH_PROGRESS	0x0040  /* show progress bar if stderr is tty */
 int refresh_index(struct index_state *, unsigned int flags, const struct pathspec *pathspec, char *seen, const char *header_msg);
+/*
+ * Refresh the index and write it to disk.
+ *
+ * 'refresh_flags' is passed directly to 'refresh_index()', while
+ * 'COMMIT_LOCK | write_flags' is passed to 'write_locked_index()', so
+ * the lockfile is always either committed or rolled back.
+ *
+ * If 'gentle' is passed, errors locking the index are ignored.
+ *
+ * Return 1 if refreshing the index returns an error, -1 if writing
+ * the index to disk fails, 0 on success.
+ *
+ * Note that if refreshing the index returns an error, we still write
+ * out the index (unless locking fails).
+ */
+int repo_refresh_and_write_index(struct repository*, unsigned int refresh_flags, unsigned int write_flags, int gentle, const struct pathspec *, char *seen, const char *header_msg);
+
 struct cache_entry *refresh_cache_entry(struct index_state *, struct cache_entry *, unsigned int);
 
 void set_alternate_index_output(const char *);
diff --git a/read-cache.c b/read-cache.c
index 52ffa8a313..7e646e06c2 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1472,6 +1472,27 @@ static void show_file(const char * fmt, const char * name, int in_porcelain,
 	printf(fmt, name);
 }
 
+int repo_refresh_and_write_index(struct repository *repo,
+				 unsigned int refresh_flags,
+				 unsigned int write_flags,
+				 int gentle,
+				 const struct pathspec *pathspec,
+				 char *seen, const char *header_msg)
+{
+	struct lock_file lock_file = LOCK_INIT;
+	int fd, ret = 0;
+
+	fd = repo_hold_locked_index(repo, &lock_file, 0);
+	if (!gentle && fd < 0)
+		return -1;
+	if (refresh_index(repo->index, refresh_flags, pathspec, seen, header_msg))
+		ret = 1;
+	if (0 <= fd && write_locked_index(repo->index, &lock_file, COMMIT_LOCK | write_flags))
+		ret = -1;
+	return ret;
+}
+
+
 int refresh_index(struct index_state *istate, unsigned int flags,
 		  const struct pathspec *pathspec,
 		  char *seen, const char *header_msg)