diff --git a/Misc/NEWS.d/next/Library/2024-11-06-17-24-59.gh-issue-126316._I1Ikc.rst b/Misc/NEWS.d/next/Library/2024-11-06-17-24-59.gh-issue-126316._I1Ikc.rst
new file mode 100644
index 00000000000000..0657838fd3cacb
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-11-06-17-24-59.gh-issue-126316._I1Ikc.rst
@@ -0,0 +1,3 @@
+:mod:`grp`: :func:`grp.getgrall` now uses ``getgrent_r()``, if the function
+is available, to make :func:`grp.getgrall` thread-safe. Patch by Victor
+Stinner.
diff --git a/Modules/grpmodule.c b/Modules/grpmodule.c
index f7d3e12f347ec2..cd85c58aef0f83 100644
--- a/Modules/grpmodule.c
+++ b/Modules/grpmodule.c
@@ -281,22 +281,46 @@ static PyObject *
 grp_getgrall_impl(PyObject *module)
 /*[clinic end generated code: output=585dad35e2e763d7 input=d7df76c825c367df]*/
 {
-    PyObject *d;
-    struct group *p;
-
-    if ((d = PyList_New(0)) == NULL)
+    PyObject *d = PyList_New(0);
+    if (d == NULL) {
         return NULL;
+    }
+
     setgrent();
-    while ((p = getgrent()) != NULL) {
-        PyObject *v = mkgrent(module, p);
+    while (1) {
+#ifdef HAVE_GETGRENT_R
+        struct group grp;
+        struct group *grpp;
+        char buf[4096];
+        int err = getgrent_r(&grp, buf, sizeof(buf), &grpp);
+        if (err) {
+            if (err != ENOENT) {
+                errno = err;
+                PyErr_SetFromErrno(PyExc_OSError);
+                goto error;
+            }
+            break;
+        }
+#else
+        struct group *grpp = getgrent();
+        if (grpp == NULL) {
+            break;
+        }
+#endif
+
+        PyObject *v = mkgrent(module, grpp);
         if (v == NULL || PyList_Append(d, v) != 0) {
             Py_XDECREF(v);
-            Py_DECREF(d);
-            endgrent();
-            return NULL;
+            goto error;
         }
         Py_DECREF(v);
     }
+    goto done;
+
+error:
+    Py_CLEAR(d);
+
+done:
     endgrent();
     return d;
 }
diff --git a/configure b/configure
index e529527214da29..1a4aff30f8bf12 100755
--- a/configure
+++ b/configure
@@ -18519,6 +18519,12 @@ if test "x$ac_cv_func_getgrent" = xyes
 then :
   printf "%s\n" "#define HAVE_GETGRENT 1" >>confdefs.h
 
+fi
+ac_fn_c_check_func "$LINENO" "getgrent_r" "ac_cv_func_getgrent_r"
+if test "x$ac_cv_func_getgrent_r" = xyes
+then :
+  printf "%s\n" "#define HAVE_GETGRENT_R 1" >>confdefs.h
+
 fi
 ac_fn_c_check_func "$LINENO" "getgrgid" "ac_cv_func_getgrgid"
 if test "x$ac_cv_func_getgrgid" = xyes
diff --git a/configure.ac b/configure.ac
index bc67a0596ac2b4..8b44926650d706 100644
--- a/configure.ac
+++ b/configure.ac
@@ -5181,7 +5181,7 @@ AC_CHECK_FUNCS([ \
   copy_file_range ctermid dup dup3 execv explicit_bzero explicit_memset \
   faccessat fchmod fchmodat fchown fchownat fdopendir fdwalk fexecve \
   fork fork1 fpathconf fstatat ftime ftruncate futimens futimes futimesat \
-  gai_strerror getegid geteuid getgid getgrent getgrgid getgrgid_r \
+  gai_strerror getegid geteuid getgid getgrent getgrent_r getgrgid getgrgid_r \
   getgrnam_r getgrouplist gethostname getitimer getloadavg getlogin \
   getpeername getpgid getpid getppid getpriority _getpty \
   getpwent getpwnam_r getpwuid getpwuid_r getresgid getresuid getrusage getsid getspent \
diff --git a/pyconfig.h.in b/pyconfig.h.in
index 924d86627b0e9b..6bdcc3d8e95bd2 100644
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -482,6 +482,9 @@
 /* Define to 1 if you have the `getgrent' function. */
 #undef HAVE_GETGRENT
 
+/* Define to 1 if you have the `getgrent_r' function. */
+#undef HAVE_GETGRENT_R
+
 /* Define to 1 if you have the `getgrgid' function. */
 #undef HAVE_GETGRGID