diff --git a/libcutils/Android.bp b/libcutils/Android.bp
index d7413d1..9cba109 100644
--- a/libcutils/Android.bp
+++ b/libcutils/Android.bp
@@ -20,7 +20,7 @@
 libcutils_nonwindows_sources = [
     "android_get_control_file.cpp",
     "fs.cpp",
-    "multiuser.c",
+    "multiuser.cpp",
     "socket_inaddr_any_server_unix.cpp",
     "socket_local_client_unix.cpp",
     "socket_local_server_unix.cpp",
diff --git a/libcutils/multiuser.c b/libcutils/multiuser.cpp
similarity index 90%
rename from libcutils/multiuser.c
rename to libcutils/multiuser.cpp
index 61403f4..0fd3d0c 100644
--- a/libcutils/multiuser.c
+++ b/libcutils/multiuser.cpp
@@ -53,9 +53,11 @@
     }
 }
 
-gid_t multiuser_get_shared_gid(userid_t user_id, appid_t app_id) {
+gid_t multiuser_get_shared_gid(userid_t, appid_t app_id) {
     if (app_id >= AID_APP_START && app_id <= AID_APP_END) {
-        return multiuser_get_uid(user_id, (app_id - AID_APP_START) + AID_SHARED_GID_START);
+        return (app_id - AID_APP_START) + AID_SHARED_GID_START;
+    } else if (app_id >= AID_ROOT && app_id <= AID_APP_START) {
+        return app_id;
     } else {
         return -1;
     }
diff --git a/libcutils/tests/multiuser_test.cpp b/libcutils/tests/multiuser_test.cpp
index 2f9d854..4b0fd13 100644
--- a/libcutils/tests/multiuser_test.cpp
+++ b/libcutils/tests/multiuser_test.cpp
@@ -57,7 +57,10 @@
     EXPECT_EQ(ERR_GID, multiuser_get_cache_gid(0, 1000));
     EXPECT_EQ(20000U, multiuser_get_cache_gid(0, 10000));
     EXPECT_EQ(ERR_GID, multiuser_get_cache_gid(0, 50000));
+    EXPECT_EQ(ERR_GID, multiuser_get_cache_gid(10, 0));
+    EXPECT_EQ(ERR_GID, multiuser_get_cache_gid(10, 1000));
     EXPECT_EQ(1020000U, multiuser_get_cache_gid(10, 10000));
+    EXPECT_EQ(ERR_GID, multiuser_get_cache_gid(10, 50000));
 }
 
 TEST(MultiuserTest, TestExt) {
@@ -77,9 +80,12 @@
 }
 
 TEST(MultiuserTest, TestShared) {
-    EXPECT_EQ(ERR_GID, multiuser_get_shared_gid(0, 0));
-    EXPECT_EQ(ERR_GID, multiuser_get_shared_gid(0, 1000));
+    EXPECT_EQ(0U, multiuser_get_shared_gid(0, 0));
+    EXPECT_EQ(1000U, multiuser_get_shared_gid(0, 1000));
     EXPECT_EQ(50000U, multiuser_get_shared_gid(0, 10000));
     EXPECT_EQ(ERR_GID, multiuser_get_shared_gid(0, 50000));
-    EXPECT_EQ(1050000U, multiuser_get_shared_gid(10, 10000));
+    EXPECT_EQ(0U, multiuser_get_shared_gid(10, 0));
+    EXPECT_EQ(1000U, multiuser_get_shared_gid(10, 1000));
+    EXPECT_EQ(50000U, multiuser_get_shared_gid(10, 10000));
+    EXPECT_EQ(ERR_GID, multiuser_get_shared_gid(10, 50000));
 }