diff --git a/builtin/commit.c b/builtin/commit.c
index cbc9613ec6..b9ab5ef314 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -255,8 +255,9 @@ static int list_paths(struct string_list *list, const char *with_tree,
 	m = xcalloc(1, i);
 
 	if (with_tree) {
-		const char *max_prefix = pathspec_prefix(prefix, pattern);
-		overlay_tree_on_cache(with_tree, max_prefix);
+		char *max_prefix = common_prefix(pattern);
+		overlay_tree_on_cache(with_tree, max_prefix ? max_prefix : prefix);
+		free(max_prefix);
 	}
 
 	for (i = 0; i < active_nr; i++) {
diff --git a/builtin/ls-files.c b/builtin/ls-files.c
index e8a800d3ac..7cff175745 100644
--- a/builtin/ls-files.c
+++ b/builtin/ls-files.c
@@ -545,7 +545,7 @@ 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, pathspec);
+	max_prefix = common_prefix(pathspec);
 	max_prefix_len = max_prefix ? strlen(max_prefix) : 0;
 
 	/* Treat unmatching pathspec elements as errors */
diff --git a/cache.h b/cache.h
index c989f79835..1aa682d83d 100644
--- a/cache.h
+++ b/cache.h
@@ -445,7 +445,6 @@ 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/dir.c b/dir.c
index 08281d2ef7..6c0d782579 100644
--- a/dir.c
+++ b/dir.c
@@ -34,49 +34,54 @@ int fnmatch_icase(const char *pattern, const char *string, int flags)
 	return fnmatch(pattern, string, flags | (ignore_case ? FNM_CASEFOLD : 0));
 }
 
-static int common_prefix(const char **pathspec)
+static size_t common_prefix_len(const char **pathspec)
 {
-	const char *path, *slash, *next;
-	int prefix;
+	const char *n, *first;
+	size_t max = 0;
 
 	if (!pathspec)
-		return 0;
+		return max;
 
-	path = *pathspec;
-	slash = strrchr(path, '/');
-	if (!slash)
-		return 0;
-
-	/*
-	 * The first 'prefix' characters of 'path' are common leading
-	 * path components among the pathspecs we have seen so far,
-	 * including the trailing slash.
-	 */
-	prefix = slash - path + 1;
-	while ((next = *++pathspec) != NULL) {
-		int len, last_matching_slash = -1;
-		for (len = 0; len < prefix && next[len] == path[len]; len++)
-			if (next[len] == '/')
-				last_matching_slash = len;
-		if (len == prefix)
-			continue;
-		if (last_matching_slash < 0)
-			return 0;
-		prefix = last_matching_slash + 1;
+	first = *pathspec;
+	while ((n = *pathspec++)) {
+		size_t i, len = 0;
+		for (i = 0; first == n || i < max; i++) {
+			char c = n[i];
+			if (!c || c != first[i] || is_glob_special(c))
+				break;
+			if (c == '/')
+				len = i + 1;
+		}
+		if (first == n || len < max) {
+			max = len;
+			if (!max)
+				break;
+		}
 	}
-	return prefix;
+	return max;
+}
+
+/*
+ * Returns a copy of the longest leading path common among all
+ * pathspecs.
+ */
+char *common_prefix(const char **pathspec)
+{
+	unsigned long len = common_prefix_len(pathspec);
+
+	return len ? xmemdupz(*pathspec, len) : NULL;
 }
 
 int fill_directory(struct dir_struct *dir, const char **pathspec)
 {
 	const char *path;
-	int len;
+	size_t len;
 
 	/*
 	 * Calculate common prefix for the pathspec, and
 	 * use that to optimize the directory walk
 	 */
-	len = common_prefix(pathspec);
+	len = common_prefix_len(pathspec);
 	path = "";
 
 	if (len)
@@ -84,6 +89,8 @@ int fill_directory(struct dir_struct *dir, const char **pathspec)
 
 	/* Read the directory and prune it */
 	read_directory(dir, path, len, pathspec);
+	if (*path)
+		free((char *)path);
 	return len;
 }
 
diff --git a/dir.h b/dir.h
index 433b5b4cd4..dd6947e1d4 100644
--- a/dir.h
+++ b/dir.h
@@ -64,6 +64,7 @@ struct dir_struct {
 #define MATCHED_RECURSIVELY 1
 #define MATCHED_FNMATCH 2
 #define MATCHED_EXACTLY 3
+extern char *common_prefix(const char **pathspec);
 extern int match_pathspec(const char **pathspec, const char *name, int namelen, int prefix, char *seen);
 extern int match_pathspec_depth(const struct pathspec *pathspec,
 				const char *name, int namelen,
diff --git a/setup.c b/setup.c
index b2b4872b70..61c22e6bec 100644
--- a/setup.c
+++ b/setup.c
@@ -236,38 +236,6 @@ 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: