diff --git a/builtin/add.c b/builtin/add.c
index bf01d89e28..9e5a80cc6f 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -534,10 +534,9 @@ int cmd_add(int argc, const char **argv, const char *prefix)
 	unplug_bulk_checkin();
 
 finish:
-	if (active_cache_changed) {
-		if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
-			die(_("Unable to write new index file"));
-	}
+	if (write_locked_index(&the_index, &lock_file,
+			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
+		die(_("Unable to write new index file"));
 
 	UNLEAK(pathspec);
 	UNLEAK(dir);
diff --git a/builtin/commit.c b/builtin/commit.c
index e8e8d13be4..ff6dac4b9c 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -389,13 +389,9 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 		if (active_cache_changed
 		    || !cache_tree_fully_valid(active_cache_tree))
 			update_main_cache_tree(WRITE_TREE_SILENT);
-		if (active_cache_changed) {
-			if (write_locked_index(&the_index, &index_lock,
-					       COMMIT_LOCK))
-				die(_("unable to write new_index file"));
-		} else {
-			rollback_lock_file(&index_lock);
-		}
+		if (write_locked_index(&the_index, &index_lock,
+				       COMMIT_LOCK | SKIP_IF_UNCHANGED))
+			die(_("unable to write new_index file"));
 		commit_style = COMMIT_AS_IS;
 		ret = get_index_file();
 		goto out;
diff --git a/builtin/merge.c b/builtin/merge.c
index 92ba99a1a5..7efa3c041d 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -651,10 +651,9 @@ static int try_merge_strategy(const char *strategy, struct commit_list *common,
 
 	hold_locked_index(&lock, LOCK_DIE_ON_ERROR);
 	refresh_cache(REFRESH_QUIET);
-	if (active_cache_changed &&
-	    write_locked_index(&the_index, &lock, COMMIT_LOCK))
+	if (write_locked_index(&the_index, &lock,
+			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
 		return error(_("Unable to write index."));
-	rollback_lock_file(&lock);
 
 	if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree")) {
 		int clean, x;
@@ -691,10 +690,9 @@ static int try_merge_strategy(const char *strategy, struct commit_list *common,
 				remoteheads->item, reversed, &result);
 		if (clean < 0)
 			exit(128);
-		if (active_cache_changed &&
-		    write_locked_index(&the_index, &lock, COMMIT_LOCK))
+		if (write_locked_index(&the_index, &lock,
+				       COMMIT_LOCK | SKIP_IF_UNCHANGED))
 			die (_("unable to write %s"), get_index_file());
-		rollback_lock_file(&lock);
 		return clean ? 0 : 1;
 	} else {
 		return try_merge_command(strategy, xopts_nr, xopts,
@@ -810,10 +808,9 @@ static int merge_trivial(struct commit *head, struct commit_list *remoteheads)
 
 	hold_locked_index(&lock, LOCK_DIE_ON_ERROR);
 	refresh_cache(REFRESH_QUIET);
-	if (active_cache_changed &&
-	    write_locked_index(&the_index, &lock, COMMIT_LOCK))
+	if (write_locked_index(&the_index, &lock,
+			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
 		return error(_("Unable to write index."));
-	rollback_lock_file(&lock);
 
 	write_tree_trivial(&result_tree);
 	printf(_("Wonderful.\n"));
diff --git a/builtin/mv.c b/builtin/mv.c
index cf3684d907..ae013d6d20 100644
--- a/builtin/mv.c
+++ b/builtin/mv.c
@@ -293,8 +293,8 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 	if (gitmodules_modified)
 		stage_updated_gitmodules(&the_index);
 
-	if (active_cache_changed &&
-	    write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
+	if (write_locked_index(&the_index, &lock_file,
+			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
 		die(_("Unable to write new index file"));
 
 	return 0;
diff --git a/builtin/rm.c b/builtin/rm.c
index 4a2fcca27b..5d59a0aa65 100644
--- a/builtin/rm.c
+++ b/builtin/rm.c
@@ -385,10 +385,9 @@ int cmd_rm(int argc, const char **argv, const char *prefix)
 			stage_updated_gitmodules(&the_index);
 	}
 
-	if (active_cache_changed) {
-		if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
-			die(_("Unable to write new index file"));
-	}
+	if (write_locked_index(&the_index, &lock_file,
+			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
+		die(_("Unable to write new index file"));
 
 	return 0;
 }
diff --git a/cache.h b/cache.h
index 21fbcc2414..5c880318e0 100644
--- a/cache.h
+++ b/cache.h
@@ -599,6 +599,7 @@ extern int read_index_unmerged(struct index_state *);
 
 /* For use with `write_locked_index()`. */
 #define COMMIT_LOCK		(1 << 0)
+#define SKIP_IF_UNCHANGED	(1 << 1)
 
 /*
  * Write the index while holding an already-taken lock. Close the lock,
@@ -615,6 +616,9 @@ extern int read_index_unmerged(struct index_state *);
  * With `COMMIT_LOCK`, the lock is always committed or rolled back.
  * Without it, the lock is closed, but neither committed nor rolled
  * back.
+ *
+ * If `SKIP_IF_UNCHANGED` is given and the index is unchanged, nothing
+ * is written (and the lock is rolled back if `COMMIT_LOCK` is given).
  */
 extern int write_locked_index(struct index_state *, struct lock_file *lock, unsigned flags);
 
diff --git a/merge-recursive.c b/merge-recursive.c
index 129577987b..2f232ad3b4 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -2223,10 +2223,9 @@ int merge_recursive_generic(struct merge_options *o,
 		return clean;
 	}
 
-	if (active_cache_changed &&
-	    write_locked_index(&the_index, &lock, COMMIT_LOCK))
+	if (write_locked_index(&the_index, &lock,
+			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
 		return err(o, _("Unable to write index."));
-	rollback_lock_file(&lock);
 
 	return clean ? 0 : 1;
 }
diff --git a/read-cache.c b/read-cache.c
index 28bf0db9d9..e2a939a5d2 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2538,6 +2538,12 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
 	int new_shared_index, ret;
 	struct split_index *si = istate->split_index;
 
+	if ((flags & SKIP_IF_UNCHANGED) && !istate->cache_changed) {
+		if (flags & COMMIT_LOCK)
+			rollback_lock_file(lock);
+		return 0;
+	}
+
 	if (istate->fsmonitor_last_update)
 		fill_fsmonitor_bitmap(istate);
 
diff --git a/rerere.c b/rerere.c
index 79203c6c1e..ea24d4c2f4 100644
--- a/rerere.c
+++ b/rerere.c
@@ -719,11 +719,9 @@ static void update_paths(struct string_list *update)
 			item->string);
 	}
 
-	if (active_cache_changed) {
-		if (write_locked_index(&the_index, &index_lock, COMMIT_LOCK))
-			die("Unable to write new index file");
-	} else
-		rollback_lock_file(&index_lock);
+	if (write_locked_index(&the_index, &index_lock,
+			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
+		die("Unable to write new index file");
 }
 
 static void remove_variant(struct rerere_id *id)
diff --git a/sequencer.c b/sequencer.c
index 548ad997b5..6ee251849d 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -517,15 +517,14 @@ static int do_recursive_merge(struct commit *base, struct commit *next,
 		return clean;
 	}
 
-	if (active_cache_changed &&
-	    write_locked_index(&the_index, &index_lock, COMMIT_LOCK))
+	if (write_locked_index(&the_index, &index_lock,
+			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
 		/*
 		 * TRANSLATORS: %s will be "revert", "cherry-pick" or
 		 * "rebase -i".
 		 */
 		return error(_("%s: Unable to write new index file"),
 			_(action_name(opts)));
-	rollback_lock_file(&index_lock);
 
 	if (!clean)
 		append_conflicts_hint(msgbuf);
@@ -1713,13 +1712,13 @@ static int read_and_refresh_cache(struct replay_opts *opts)
 			_(action_name(opts)));
 	}
 	refresh_index(&the_index, REFRESH_QUIET|REFRESH_UNMERGED, NULL, NULL, NULL);
-	if (the_index.cache_changed && index_fd >= 0) {
-		if (write_locked_index(&the_index, &index_lock, COMMIT_LOCK)) {
+	if (index_fd >= 0) {
+		if (write_locked_index(&the_index, &index_lock,
+				       COMMIT_LOCK | SKIP_IF_UNCHANGED)) {
 			return error(_("git %s: failed to refresh the index"),
 				_(action_name(opts)));
 		}
 	}
-	rollback_lock_file(&index_lock);
 	return 0;
 }