diff --git a/Userland/su.cpp b/Userland/su.cpp
index 8f7a10aa82..f600179b78 100644
--- a/Userland/su.cpp
+++ b/Userland/su.cpp
@@ -1,3 +1,4 @@
+#include <AK/Vector.h>
 #include <alloca.h>
 #include <grp.h>
 #include <pwd.h>
@@ -10,8 +11,9 @@ int main(int argc, char** argv)
 {
     uid_t uid = 0;
     gid_t gid = 0;
+    struct passwd* pwd = nullptr;
     if (argc > 1) {
-        auto* pwd = getpwnam(argv[1]);
+        pwd = getpwnam(argv[1]);
         if (!pwd) {
             fprintf(stderr, "No such user: %s\n", argv[1]);
             return 1;
@@ -19,7 +21,30 @@ int main(int argc, char** argv)
         uid = pwd->pw_uid;
         gid = pwd->pw_gid;
     }
-    int rc = setgid(uid);
+
+    if (!pwd)
+        pwd = getpwuid(0);
+
+    if (!pwd) {
+        fprintf(stderr, "No passwd entry.\n");
+        return 1;
+    }
+
+    Vector<gid_t> extra_gids;
+    for (auto* group = getgrent(); group; group = getgrent()) {
+        for (size_t i = 0; group->gr_mem[i]; ++i) {
+            if (!strcmp(pwd->pw_name, group->gr_mem[i]))
+                extra_gids.append(group->gr_gid);
+        }
+    }
+    endgrent();
+
+    int rc = setgroups(extra_gids.size(), extra_gids.data());
+    if (rc < 0) {
+        perror("setgroups");
+        return 1;
+    }
+    rc = setgid(uid);
     if (rc < 0) {
         perror("setgid");
         return 1;