diff --git a/builtin/commit.c b/builtin/commit.c
index e1af9b19f0..cb738574f7 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -256,8 +256,10 @@ static int list_paths(struct string_list *list, const char *with_tree,
 		;
 	m = xcalloc(1, i);
 
-	if (with_tree)
-		overlay_tree_on_cache(with_tree, prefix);
+	if (with_tree) {
+		const char *max_prefix = pathspec_prefix(prefix, pattern);
+		overlay_tree_on_cache(with_tree, max_prefix);
+	}
 
 	for (i = 0; i < active_nr; i++) {
 		struct cache_entry *ce = active_cache[i];
diff --git a/builtin/ls-files.c b/builtin/ls-files.c
index 15701233e2..0e98bff0c4 100644
--- a/builtin/ls-files.c
+++ b/builtin/ls-files.c
@@ -276,41 +276,6 @@ static void prune_cache(const char *prefix)
 	active_nr = last;
 }
 
-static const char *pathspec_prefix(const char *prefix)
-{
-	const char **p, *n, *prev;
-	unsigned long max;
-
-	if (!pathspec) {
-		max_prefix_len = prefix ? strlen(prefix) : 0;
-		return prefix;
-	}
-
-	prev = NULL;
-	max = PATH_MAX;
-	for (p = pathspec; (n = *p) != NULL; p++) {
-		int i, len = 0;
-		for (i = 0; i < max; i++) {
-			char c = n[i];
-			if (prev && prev[i] != c)
-				break;
-			if (!c || c == '*' || c == '?')
-				break;
-			if (c == '/')
-				len = i+1;
-		}
-		prev = n;
-		if (len < max) {
-			max = len;
-			if (!max)
-				break;
-		}
-	}
-
-	max_prefix_len = max;
-	return max ? xmemdupz(prev, max) : NULL;
-}
-
 static void strip_trailing_slash_from_submodules(void)
 {
 	const char **p;
@@ -576,7 +541,8 @@ int cmd_ls_files(int argc, const char **argv, const char *cmd_prefix)
 		strip_trailing_slash_from_submodules();
 
 	/* Find common prefix for all pathspec's */
-	max_prefix = pathspec_prefix(prefix);
+	max_prefix = pathspec_prefix(prefix, pathspec);
+	max_prefix_len = max_prefix ? strlen(max_prefix) : 0;
 
 	/* Treat unmatching pathspec elements as errors */
 	if (pathspec && error_unmatch) {
diff --git a/cache.h b/cache.h
index f49eaf9263..b33ba73197 100644
--- a/cache.h
+++ b/cache.h
@@ -441,6 +441,7 @@ extern void set_git_work_tree(const char *tree);
 #define ALTERNATE_DB_ENVIRONMENT "GIT_ALTERNATE_OBJECT_DIRECTORIES"
 
 extern const char **get_pathspec(const char *prefix, const char **pathspec);
+extern const char *pathspec_prefix(const char *prefix, const char **pathspec);
 extern void setup_work_tree(void);
 extern const char *setup_git_directory_gently(int *);
 extern const char *setup_git_directory(void);
diff --git a/setup.c b/setup.c
index 5ea5502e48..2c51a9a4c7 100644
--- a/setup.c
+++ b/setup.c
@@ -264,6 +264,38 @@ const char **get_pathspec(const char *prefix, const char **pathspec)
 	return pathspec;
 }
 
+const char *pathspec_prefix(const char *prefix, const char **pathspec)
+{
+	const char **p, *n, *prev;
+	unsigned long max;
+
+	if (!pathspec)
+		return prefix ? xmemdupz(prefix, strlen(prefix)) : NULL;
+
+	prev = NULL;
+	max = PATH_MAX;
+	for (p = pathspec; (n = *p) != NULL; p++) {
+		int i, len = 0;
+		for (i = 0; i < max; i++) {
+			char c = n[i];
+			if (prev && prev[i] != c)
+				break;
+			if (!c || c == '*' || c == '?')
+				break;
+			if (c == '/')
+				len = i+1;
+		}
+		prev = n;
+		if (len < max) {
+			max = len;
+			if (!max)
+				break;
+		}
+	}
+
+	return max ? xmemdupz(prev, max) : NULL;
+}
+
 /*
  * Test if it looks like we're at a git directory.
  * We want to see: