diff --git a/read-cache.c b/read-cache.c
index fc80d7982b81bf..5baf652a547694 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1278,6 +1278,11 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 	int skip_df_check = option & ADD_CACHE_SKIP_DFCHECK;
 	int new_only = option & ADD_CACHE_NEW_ONLY;
 
+#ifdef GIT_WINDOWS_NATIVE
+	if (protect_ntfs && strchr(ce->name, '\\'))
+		return error(_("filename in tree entry contains backslash: '%s'"), ce->name);
+#endif
+
 	if (!(option & ADD_CACHE_KEEP_CACHE_TREE))
 		cache_tree_invalidate_path(istate, ce->name);
 
diff --git a/t/t7415-submodule-names.sh b/t/t7415-submodule-names.sh
index 905a557585afdb..7ae0dc8ff47ee7 100755
--- a/t/t7415-submodule-names.sh
+++ b/t/t7415-submodule-names.sh
@@ -207,6 +207,9 @@ test_expect_success MINGW 'prevent git~1 squatting on Windows' '
 			git hash-object -w --stdin)" &&
 		rev="$(git rev-parse --verify HEAD)" &&
 		hash="$(echo x | git hash-object -w --stdin)" &&
+		test_must_fail git update-index --add \
+			--cacheinfo 160000,$rev,d\\a 2>err &&
+		test_i18ngrep backslash err &&
 		git -c core.protectNTFS=false update-index --add \
 			--cacheinfo 100644,$modules,.gitmodules \
 			--cacheinfo 160000,$rev,c \
@@ -214,9 +217,7 @@ test_expect_success MINGW 'prevent git~1 squatting on Windows' '
 			--cacheinfo 100644,$hash,d./a/x \
 			--cacheinfo 100644,$hash,d./a/..git &&
 		test_tick &&
-		git -c core.protectNTFS=false commit -m "module" &&
-		test_must_fail git show HEAD: 2>err &&
-		test_i18ngrep backslash err
+		git -c core.protectNTFS=false commit -m "module"
 	) &&
 	test_must_fail git -c core.protectNTFS=false \
 		clone --recurse-submodules squatting squatting-clone 2>err &&
diff --git a/tree-walk.c b/tree-walk.c
index 31cec2a08dc6a4..bea819d826fb1c 100644
--- a/tree-walk.c
+++ b/tree-walk.c
@@ -43,12 +43,6 @@ static int decode_tree_entry(struct tree_desc *desc, const char *buf, unsigned l
 		strbuf_addstr(err, _("empty filename in tree entry"));
 		return -1;
 	}
-#ifdef GIT_WINDOWS_NATIVE
-	if (protect_ntfs && strchr(path, '\\')) {
-		strbuf_addf(err, _("filename in tree entry contains backslash: '%s'"), path);
-		return -1;
-	}
-#endif
 	len = strlen(path) + 1;
 
 	/* Initialize the descriptor entry */