diff --git a/Makefile b/Makefile
index e11340c1ae..ea1156b683 100644
--- a/Makefile
+++ b/Makefile
@@ -2210,6 +2210,11 @@ ifndef HAVE_PLATFORM_PROCINFO
 	COMPAT_OBJS += compat/stub/procinfo.o
 endif
 
+ifdef NO_PATHCONF
+	COMPAT_CFLAGS += -DNO_PATHCONF
+	COMPAT_OBJS += compat/pathconf.o
+endif
+
 ifdef RUNTIME_PREFIX
 
         ifdef HAVE_BSD_KERN_PROC_SYSCTL
diff --git a/compat/pathconf.c b/compat/pathconf.c
new file mode 100644
index 0000000000..37500cfa0d
--- /dev/null
+++ b/compat/pathconf.c
@@ -0,0 +1,10 @@
+#include "git-compat-util.h"
+
+/*
+ * Minimal stub for platforms without pathconf() (e.g. Windows),
+ * to fall back to NAME_MAX from limits.h or compat/posix.h.
+ */
+long git_pathconf(const char *path UNUSED, int name UNUSED)
+{
+	return -1;
+}
diff --git a/compat/posix.h b/compat/posix.h
index 067a00f33b..aa050fd58c 100644
--- a/compat/posix.h
+++ b/compat/posix.h
@@ -250,6 +250,14 @@ char *gitdirname(char *);
 #define NAME_MAX 255
 #endif
 
+#ifdef NO_PATHCONF
+#ifndef _PC_NAME_MAX
+#define _PC_NAME_MAX 1 /* dummy value, only used for git_pathconf */
+#endif
+#define pathconf(a,b) git_pathconf(a,b)
+long git_pathconf(const char *path, int name);
+#endif
+
 typedef uintmax_t timestamp_t;
 #define PRItime PRIuMAX
 #define parse_timestamp strtoumax
diff --git a/config.mak.uname b/config.mak.uname
index 1691c6ae6e..49ba3de39d 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -473,6 +473,7 @@ ifeq ($(uname_S),Windows)
 	NEEDS_CRYPTO_WITH_SSL = YesPlease
 	NO_LIBGEN_H = YesPlease
 	NO_POLL = YesPlease
+	NO_PATHCONF = YesPlease
 	NO_SYMLINK_HEAD = YesPlease
 	NO_IPV6 = YesPlease
 	NO_SETENV = YesPlease
@@ -688,6 +689,7 @@ ifeq ($(uname_S),MINGW)
 	NEEDS_CRYPTO_WITH_SSL = YesPlease
 	NO_LIBGEN_H = YesPlease
 	NO_POLL = YesPlease
+	NO_PATHCONF = YesPlease
 	NO_SYMLINK_HEAD = YesPlease
 	NO_SETENV = YesPlease
 	NO_STRCASESTR = YesPlease
diff --git a/meson.build b/meson.build
index 5dd299b496..3ae5c391a9 100644
--- a/meson.build
+++ b/meson.build
@@ -1392,6 +1392,7 @@ checkfuncs = {
   'initgroups' : [],
   'strtoumax' : ['strtoumax.c', 'strtoimax.c'],
   'pread' : ['pread.c'],
+  'pathconf' : ['pathconf.c'],
 }
 
 if host_machine.system() == 'windows'
diff --git a/submodule.c b/submodule.c
index f8eb760215..01d6416ff2 100644
--- a/submodule.c
+++ b/submodule.c
@@ -2625,13 +2625,29 @@ void submodule_name_to_gitdir(struct strbuf *buf, struct repository *r,
 
 	if (the_repository->repository_format_submodule_encoding) {
 		struct strbuf tmp = STRBUF_INIT;
+		size_t base_len;
+		long name_max;
 
 		strbuf_reset(buf);
 		repo_git_path_append(r, buf, "modules/");
+		base_len = buf->len;
 
 		strbuf_addstr_urlencode(&tmp, submodule_name, is_rfc3986_unreserved);
 		strbuf_addstr_case_encode(buf, tmp.buf);
 
+		/* Ensure final path length is below NAME_MAX after encoding */
+		name_max = pathconf(buf->buf, _PC_NAME_MAX);
+		if (name_max == -1)
+			name_max = NAME_MAX;
+
+		if (buf->len - base_len > name_max)
+			/*
+			 * TODO: make this smarter; instead of erroring out, maybe we could trim or
+			 * shard the gitdir names to make them fit under NAME_MAX.
+			 */
+			die(_("submodule name %s is too long (%"PRIuMAX" bytes, limit %"PRIuMAX")"),
+			    buf->buf, (uintmax_t)buf->len - base_len, (uintmax_t)name_max);
+
 		strbuf_release(&tmp);
 	}
 }
diff --git a/t/t7425-submodule-encoding.sh b/t/t7425-submodule-encoding.sh
index 4ea385d882..8041781491 100755
--- a/t/t7425-submodule-encoding.sh
+++ b/t/t7425-submodule-encoding.sh
@@ -143,4 +143,20 @@ test_expect_success 'submodule git dir nesting detection must work with parallel
 	verify_submodule_gitdir_path clone_parallel hippo/hooks modules/hippo%2fhooks
 '
 
+test_expect_success 'submodule encoded name exceeds max name limit' '
+	(
+		cd main &&
+
+		# find the system NAME_MAX (fall back to 255 if unknown)
+		name_max=$(getconf NAME_MAX . 2>/dev/null || echo 255) &&
+
+		# each "%" char encodes to "%25" (3 chars), ensure we exceed NAME_MAX
+		count=$((name_max + 10)) &&
+		longname=$(test_seq -f "%%%0.s" 1 $count | tr -d "\n") &&
+
+		test_must_fail git submodule add ../new-sub "$longname" 2>err &&
+		test_grep "fatal: submodule name .* is too long" err
+	)
+'
+
 test_done