diff -ruN a/lib/getugroups.c b/lib/getugroups.c
--- a/lib/getugroups.c	2024-04-10 20:11:58.434321202 +0900
+++ b/lib/getugroups.c	2024-04-10 20:15:11.853008324 +0900
@@ -19,6 +19,9 @@
 
 #include <config.h>
 
+/* We do not need this code if getgrouplist(3) is available.  */
+#ifndef HAVE_GETGROUPLIST
+
 #include "getugroups.h"
 
 #include <errno.h>
@@ -131,3 +134,4 @@
 }
 
 #endif /* HAVE_GRP_H */
+#endif	/* have getgrouplist */
diff -ruN a/lib/mgetgroups.c b/lib/mgetgroups.c
--- a/lib/mgetgroups.c	2024-04-10 20:11:58.438321382 +0900
+++ b/lib/mgetgroups.c	2024-04-10 20:15:11.854008369 +0900
@@ -120,9 +120,17 @@
   /* else no username, so fall through and use getgroups. */
 #endif
 
-  max_n_groups = (username
-                  ? getugroups (0, NULL, username, gid)
-                  : getgroups (0, NULL));
+  if (!username)
+    max_n_groups = getgroups(0, NULL);
+  else 
+  {
+#ifdef HAVE_GETGROUPLIST
+    max_n_groups = 0;
+    getgrouplist (username, gid, NULL, &max_n_groups);
+#else
+    max_n_groups = getugroups (0, NULL, username, gid);
+#endif
+  }
 
   /* If we failed to count groups because there is no supplemental
      group support, then return an array containing just GID.
@@ -144,10 +152,25 @@
   if (g == NULL)
     return -1;
 
-  ng = (username
-        ? getugroups (max_n_groups, g, username, gid)
-        : getgroups (max_n_groups - (gid != (gid_t) -1),
-                                g + (gid != (gid_t) -1)));
+  if (!username)
+    ng = getgroups (max_n_groups - (gid != (gid_t)-1), g + (gid != (gid_t)-1));
+  else
+  {
+#ifdef HAVE_GETGROUPLIST
+    int e;
+    ng = max_n_groups;
+    while ((e = getgrouplist (username, gid, g, &ng)) == -1
+	&& ng > max_n_groups)
+    {
+      max_n_groups = ng;
+      g = xrealloc (g, max_n_groups * sizeof (GETGROUPS_T));
+    }
+    if (e == -1)
+      ng = -1;
+#else
+    ng = getugroups (max_n_groups, g, username, gid);
+#endif
+  }
 
   if (ng < 0)
     {
diff -ruN a/m4/jm-macros.m4 b/m4/jm-macros.m4
--- a/m4/jm-macros.m4	2024-01-01 22:27:23.000000000 +0900
+++ b/m4/jm-macros.m4	2024-04-10 20:16:13.349770362 +0900
@@ -67,6 +67,7 @@
     fallocate
     fchown
     fchmod
+    getgrouplist
     setgroups
     sethostname
     siginterrupt