diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 2c87ef9364fa6d..b68102bb3edf9f 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -72,16 +72,6 @@ static char *get_default_remote(void)
 	return repo_get_default_remote(the_repository);
 }
 
-static int starts_with_dot_slash(const char *str)
-{
-	return str[0] == '.' && is_dir_sep(str[1]);
-}
-
-static int starts_with_dot_dot_slash(const char *str)
-{
-	return str[0] == '.' && str[1] == '.' && is_dir_sep(str[2]);
-}
-
 /*
  * Returns 1 if it was the last chop before ':'.
  */
@@ -108,6 +98,16 @@ static int chop_last_dir(char **remoteurl, int is_relative)
 	return 0;
 }
 
+static int starts_with_dot_slash(const char *const path)
+{
+	return starts_with_dot_slash_native(path);;
+}
+
+static int starts_with_dot_dot_slash(const char *const path)
+{
+	return starts_with_dot_dot_slash_native(path);
+}
+
 /*
  * The `url` argument is the URL that navigates to the submodule origin
  * repo. When relative, this URL is relative to the superproject origin
diff --git a/compat/mingw.c b/compat/mingw.c
index 6fe80fdf014021..b94b473d97857f 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -2830,7 +2830,7 @@ int is_valid_win32_path(const char *path, int allow_literal_nul)
 			}
 
 			c = path[i];
-			if (c && c != '.' && c != ':' && c != '/' && c != '\\')
+			if (c && c != '.' && c != ':' && !is_xplatform_dir_sep(c))
 				goto not_a_reserved_name;
 
 			/* contains reserved name */
diff --git a/compat/win32/path-utils.h b/compat/win32/path-utils.h
index bba2b644080f06..65fa3b9263a47c 100644
--- a/compat/win32/path-utils.h
+++ b/compat/win32/path-utils.h
@@ -6,11 +6,7 @@ int win32_has_dos_drive_prefix(const char *path);
 
 int win32_skip_dos_drive_prefix(char **path);
 #define skip_dos_drive_prefix win32_skip_dos_drive_prefix
-static inline int win32_is_dir_sep(int c)
-{
-	return c == '/' || c == '\\';
-}
-#define is_dir_sep win32_is_dir_sep
+#define is_dir_sep is_xplatform_dir_sep
 static inline char *win32_find_last_dir_sep(const char *path)
 {
 	char *ret = NULL;
diff --git a/dir.c b/dir.c
index f2b0f242101b29..d25aa6ade5571e 100644
--- a/dir.c
+++ b/dir.c
@@ -3890,3 +3890,32 @@ void relocate_gitdir(const char *path, const char *old_git_dir, const char *new_
 
 	connect_work_tree_and_git_dir(path, new_git_dir, 0);
 }
+
+int path_match_flags(const char *const str, const enum path_match_flags flags)
+{
+	const char *p = str;
+
+	if (flags & PATH_MATCH_NATIVE &&
+	    flags & PATH_MATCH_XPLATFORM)
+		BUG("path_match_flags() must get one match kind, not multiple!");
+	else if (!(flags & PATH_MATCH_KINDS_MASK))
+		BUG("path_match_flags() must get at least one match kind!");
+
+	if (flags & PATH_MATCH_STARTS_WITH_DOT_SLASH &&
+	    flags & PATH_MATCH_STARTS_WITH_DOT_DOT_SLASH)
+		BUG("path_match_flags() must get one platform kind, not multiple!");
+	else if (!(flags & PATH_MATCH_PLATFORM_MASK))
+		BUG("path_match_flags() must get at least one platform kind!");
+
+	if (*p++ != '.')
+		return 0;
+	if (flags & PATH_MATCH_STARTS_WITH_DOT_DOT_SLASH &&
+	    *p++ != '.')
+		return 0;
+
+	if (flags & PATH_MATCH_NATIVE)
+		return is_dir_sep(*p);
+	else if (flags & PATH_MATCH_XPLATFORM)
+		return is_xplatform_dir_sep(*p);
+	BUG("unreachable");
+}
diff --git a/dir.h b/dir.h
index 8e02dfb505d163..7bc862030cfb3b 100644
--- a/dir.h
+++ b/dir.h
@@ -578,4 +578,67 @@ void connect_work_tree_and_git_dir(const char *work_tree,
 void relocate_gitdir(const char *path,
 		     const char *old_git_dir,
 		     const char *new_git_dir);
+
+/**
+ * The "enum path_matches_kind" determines how path_match_flags() will
+ * behave. The flags come in sets, and one (and only one) must be
+ * provided out of each "set":
+ *
+ * PATH_MATCH_NATIVE:
+ *	Path separator is is_dir_sep()
+ * PATH_MATCH_XPLATFORM:
+ *	Path separator is is_xplatform_dir_sep()
+ *
+ * Do we use is_dir_sep() to check for a directory separator
+ * (*_NATIVE), or do we always check for '/' or '\' (*_XPLATFORM). The
+ * "*_NATIVE" version on Windows is the same as "*_XPLATFORM",
+ * everywhere else "*_NATIVE" means "only /".
+ *
+ * PATH_MATCH_STARTS_WITH_DOT_SLASH:
+ *	Match a path starting with "./"
+ * PATH_MATCH_STARTS_WITH_DOT_DOT_SLASH:
+ *	Match a path starting with "../"
+ *
+ * The "/" in the above is adjusted based on the "*_NATIVE" and
+ * "*_XPLATFORM" flags.
+ */
+enum path_match_flags {
+	PATH_MATCH_NATIVE = 1 << 0,
+	PATH_MATCH_XPLATFORM = 1 << 1,
+	PATH_MATCH_STARTS_WITH_DOT_SLASH = 1 << 2,
+	PATH_MATCH_STARTS_WITH_DOT_DOT_SLASH = 1 << 3,
+};
+#define PATH_MATCH_KINDS_MASK (PATH_MATCH_STARTS_WITH_DOT_SLASH | \
+	PATH_MATCH_STARTS_WITH_DOT_DOT_SLASH)
+#define PATH_MATCH_PLATFORM_MASK (PATH_MATCH_NATIVE | PATH_MATCH_XPLATFORM)
+
+/**
+ * path_match_flags() checks if a given "path" matches a given "enum
+ * path_match_flags" criteria.
+ */
+int path_match_flags(const char *const path, const enum path_match_flags f);
+
+/**
+ * starts_with_dot_slash_native(): convenience wrapper for
+ * path_match_flags() with PATH_MATCH_STARTS_WITH_DOT_SLASH and
+ * PATH_MATCH_NATIVE.
+ */
+static inline int starts_with_dot_slash_native(const char *const path)
+{
+	const enum path_match_flags what = PATH_MATCH_STARTS_WITH_DOT_SLASH;
+
+	return path_match_flags(path, what | PATH_MATCH_NATIVE);
+}
+
+/**
+ * starts_with_dot_slash_native(): convenience wrapper for
+ * path_match_flags() with PATH_MATCH_STARTS_WITH_DOT_DOT_SLASH and
+ * PATH_MATCH_NATIVE.
+ */
+static inline int starts_with_dot_dot_slash_native(const char *const path)
+{
+	const enum path_match_flags what = PATH_MATCH_STARTS_WITH_DOT_DOT_SLASH;
+
+	return path_match_flags(path, what | PATH_MATCH_NATIVE);
+}
 #endif
diff --git a/fsck.c b/fsck.c
index 3ec500d707aaf6..dd4822ba1be7fe 100644
--- a/fsck.c
+++ b/fsck.c
@@ -975,27 +975,16 @@ int fsck_tag_standalone(const struct object_id *oid, const char *buffer,
 	return ret;
 }
 
-/*
- * Like builtin/submodule--helper.c's starts_with_dot_slash, but without
- * relying on the platform-dependent is_dir_sep helper.
- *
- * This is for use in checking whether a submodule URL is interpreted as
- * relative to the current directory on any platform, since \ is a
- * directory separator on Windows but not on other platforms.
- */
-static int starts_with_dot_slash(const char *str)
+static int starts_with_dot_slash(const char *const path)
 {
-	return str[0] == '.' && (str[1] == '/' || str[1] == '\\');
+	return path_match_flags(path, PATH_MATCH_STARTS_WITH_DOT_SLASH |
+				PATH_MATCH_XPLATFORM);
 }
 
-/*
- * Like starts_with_dot_slash, this is a variant of submodule--helper's
- * helper of the same name with the twist that it accepts backslash as a
- * directory separator even on non-Windows platforms.
- */
-static int starts_with_dot_dot_slash(const char *str)
+static int starts_with_dot_dot_slash(const char *const path)
 {
-	return str[0] == '.' && starts_with_dot_slash(str + 1);
+	return path_match_flags(path, PATH_MATCH_STARTS_WITH_DOT_DOT_SLASH |
+				PATH_MATCH_XPLATFORM);
 }
 
 static int submodule_url_is_relative(const char *url)
diff --git a/git-compat-util.h b/git-compat-util.h
index 58fd813bd012f1..ba3436db9a1d0a 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -236,6 +236,12 @@
 #include <sys/sysctl.h>
 #endif
 
+/* Used by compat/win32/path-utils.h, and more */
+static inline int is_xplatform_dir_sep(int c)
+{
+	return c == '/' || c == '\\';
+}
+
 #if defined(__CYGWIN__)
 #include "compat/win32/path-utils.h"
 #endif
@@ -416,11 +422,11 @@ static inline int git_skip_dos_drive_prefix(char **path)
 #define skip_dos_drive_prefix git_skip_dos_drive_prefix
 #endif
 
-#ifndef is_dir_sep
 static inline int git_is_dir_sep(int c)
 {
 	return c == '/';
 }
+#ifndef is_dir_sep
 #define is_dir_sep git_is_dir_sep
 #endif
 
diff --git a/path.c b/path.c
index d73146b6cd266a..2ab78278943a1d 100644
--- a/path.c
+++ b/path.c
@@ -1413,7 +1413,7 @@ int is_ntfs_dotgit(const char *name)
 
 	for (;;) {
 		c = *(name++);
-		if (!c || c == '\\' || c == '/' || c == ':')
+		if (!c || is_xplatform_dir_sep(c) || c == ':')
 			return 1;
 		if (c != '.' && c != ' ')
 			return 0;
diff --git a/submodule-config.c b/submodule-config.c
index 29668b0620dd91..ce3beaf5d4f0d6 100644
--- a/submodule-config.c
+++ b/submodule-config.c
@@ -204,17 +204,17 @@ int check_submodule_name(const char *name)
 		return -1;
 
 	/*
-	 * Look for '..' as a path component. Check both '/' and '\\' as
+	 * Look for '..' as a path component. Check is_xplatform_dir_sep() as
 	 * separators rather than is_dir_sep(), because we want the name rules
 	 * to be consistent across platforms.
 	 */
 	goto in_component; /* always start inside component */
 	while (*name) {
 		char c = *name++;
-		if (c == '/' || c == '\\') {
+		if (is_xplatform_dir_sep(c)) {
 in_component:
 			if (name[0] == '.' && name[1] == '.' &&
-			    (!name[2] || name[2] == '/' || name[2] == '\\'))
+			    (!name[2] || is_xplatform_dir_sep(name[2])))
 				return -1;
 		}
 	}