diff --git a/apply.c b/apply.c
index c49cef0637..854faa6779 100644
--- a/apply.c
+++ b/apply.c
@@ -3741,7 +3741,7 @@ static int check_to_create(struct apply_state *state,
 			return 0;
 
 		return EXISTS_IN_WORKTREE;
-	} else if ((errno != ENOENT) && (errno != ENOTDIR)) {
+	} else if (!is_missing_file_error(errno)) {
 		return error_errno("%s", new_name);
 	}
 	return 0;
diff --git a/builtin/rm.c b/builtin/rm.c
index 7c323d0123..b39f10fcb6 100644
--- a/builtin/rm.c
+++ b/builtin/rm.c
@@ -129,7 +129,7 @@ static int check_local_mod(struct object_id *head, int index_only)
 		ce = active_cache[pos];
 
 		if (lstat(ce->name, &st) < 0) {
-			if (errno != ENOENT && errno != ENOTDIR)
+			if (!is_missing_file_error(errno))
 				warning_errno(_("failed to stat '%s'"), ce->name);
 			/* It already vanished from the working tree */
 			continue;
diff --git a/builtin/update-index.c b/builtin/update-index.c
index ebfc09faa0..f99b1e5790 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -257,7 +257,7 @@ static int remove_one_path(const char *path)
  */
 static int process_lstat_error(const char *path, int err)
 {
-	if (err == ENOENT || err == ENOTDIR)
+	if (is_missing_file_error(err))
 		return remove_one_path(path);
 	return error("lstat(\"%s\"): %s", path, strerror(err));
 }
diff --git a/diff-lib.c b/diff-lib.c
index 2982bf055a..76c8f185cd 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -29,7 +29,7 @@
 static int check_removed(const struct cache_entry *ce, struct stat *st)
 {
 	if (lstat(ce->name, st) < 0) {
-		if (errno != ENOENT && errno != ENOTDIR)
+		if (!is_missing_file_error(errno))
 			return -1;
 		return 1;
 	}
diff --git a/dir.c b/dir.c
index 9efcf1eab6..70f2de38f2 100644
--- a/dir.c
+++ b/dir.c
@@ -2337,7 +2337,7 @@ int remove_path(const char *name)
 {
 	char *slash;
 
-	if (unlink(name) && errno != ENOENT && errno != ENOTDIR)
+	if (unlink(name) && !is_missing_file_error(errno))
 		return -1;
 
 	slash = strrchr(name, '/');
diff --git a/git-compat-util.h b/git-compat-util.h
index 4b7dcf21ad..e83fd2eb07 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -1134,6 +1134,21 @@ struct tm *git_gmtime_r(const time_t *, struct tm *);
 #define getc_unlocked(fh) getc(fh)
 #endif
 
+/*
+ * Our code often opens a path to an optional file, to work on its
+ * contents when we can successfully open it.  We can ignore a failure
+ * to open if such an optional file does not exist, but we do want to
+ * report a failure in opening for other reasons (e.g. we got an I/O
+ * error, or the file is there, but we lack the permission to open).
+ *
+ * Call this function after seeing an error from open() or fopen() to
+ * see if the errno indicates a missing file that we can safely ignore.
+ */
+static inline int is_missing_file_error(int errno_)
+{
+	return (errno_ == ENOENT || errno_ == ENOTDIR);
+}
+
 extern int cmd_main(int, const char **);
 
 #endif
diff --git a/setup.c b/setup.c
index e3f7699a90..ba6e855178 100644
--- a/setup.c
+++ b/setup.c
@@ -150,7 +150,7 @@ int check_filename(const char *prefix, const char *arg)
 		free(to_free);
 		return 1; /* file exists */
 	}
-	if (errno == ENOENT || errno == ENOTDIR) {
+	if (is_missing_file_error(errno)) {
 		free(to_free);
 		return 0; /* file does not exist */
 	}
diff --git a/sha1_name.c b/sha1_name.c
index e9ffe685d5..5126853bb5 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -1408,7 +1408,7 @@ static void diagnose_invalid_sha1_path(const char *prefix,
 	if (file_exists(filename))
 		die("Path '%s' exists on disk, but not in '%.*s'.",
 		    filename, object_name_len, object_name);
-	if (errno == ENOENT || errno == ENOTDIR) {
+	if (is_missing_file_error(errno)) {
 		char *fullname = xstrfmt("%s%s", prefix, filename);
 
 		if (!get_tree_entry(tree_sha1, fullname,
@@ -1473,7 +1473,7 @@ static void diagnose_invalid_index_path(int stage,
 
 	if (file_exists(filename))
 		die("Path '%s' exists on disk, but not in the index.", filename);
-	if (errno == ENOENT || errno == ENOTDIR)
+	if (is_missing_file_error(errno))
 		die("Path '%s' does not exist (neither on disk nor in the index).",
 		    filename);
 
diff --git a/wrapper.c b/wrapper.c
index d837417709..708e98a965 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -583,8 +583,8 @@ void warn_on_inaccessible(const char *path)
 
 static int access_error_is_ok(int err, unsigned flag)
 {
-	return err == ENOENT || err == ENOTDIR ||
-		((flag & ACCESS_EACCES_OK) && err == EACCES);
+	return (is_missing_file_error(err) ||
+		((flag & ACCESS_EACCES_OK) && err == EACCES));
 }
 
 int access_or_warn(const char *path, int mode, unsigned flag)