diff --git a/src/fileops.c b/src/fileops.c
index 63aedc6d0..17007f823 100644
--- a/src/fileops.c
+++ b/src/fileops.c
@@ -147,7 +147,13 @@ int git_futils_readbuffer_updated(
 	if (p_stat(path, &st) < 0)
 		return git_path_set_error(errno, path, "stat");
 
-	if (S_ISDIR(st.st_mode) || !git__is_sizet(st.st_size+1)) {
+
+	if (S_ISDIR(st.st_mode)) {
+		giterr_set(GITERR_INVALID, "requested file is a directory");
+		return GIT_ENOTFOUND;
+	}
+
+	if (!git__is_sizet(st.st_size+1)) {
 		giterr_set(GITERR_OS, "Invalid regular file stat for '%s'", path);
 		return -1;
 	}
diff --git a/tests-clar/refs/lookup.c b/tests-clar/refs/lookup.c
index 0dbebc5c2..2e31cf0f6 100644
--- a/tests-clar/refs/lookup.c
+++ b/tests-clar/refs/lookup.c
@@ -46,3 +46,15 @@ void test_refs_lookup__oid(void)
 	cl_git_pass(git_oid_fromstr(&expected, "1385f264afb75a56a5bec74243be9b367ba4ca08"));
 	cl_assert(git_oid_cmp(&tag, &expected) == 0);
 }
+
+void test_refs_lookup__namespace(void)
+{
+	int error;
+	git_reference *ref;
+
+	error = git_reference_lookup(&ref, g_repo, "refs/heads");
+	cl_assert_equal_i(error, GIT_ENOTFOUND);
+
+	error = git_reference_lookup(&ref, g_repo, "refs/heads/");
+	cl_assert_equal_i(error, GIT_EINVALIDSPEC);
+}