diff --git a/Tests/LibC/CMakeLists.txt b/Tests/LibC/CMakeLists.txt
index 25719f945b..18b60fb65a 100644
--- a/Tests/LibC/CMakeLists.txt
+++ b/Tests/LibC/CMakeLists.txt
@@ -5,6 +5,7 @@ set(TEST_SOURCES
     TestEnvironment.cpp
     TestIo.cpp
     TestLibCExec.cpp
+    TestLibCGrp.cpp
     TestLibCDirEnt.cpp
     TestLibCInodeWatcher.cpp
     TestLibCMkTemp.cpp
diff --git a/Tests/LibC/TestLibCGrp.cpp b/Tests/LibC/TestLibCGrp.cpp
new file mode 100644
index 0000000000..22fa7de269
--- /dev/null
+++ b/Tests/LibC/TestLibCGrp.cpp
@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) 2018-2023, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/ByteString.h>
+#include <AK/HashTable.h>
+#include <LibTest/Macros.h>
+#include <LibTest/TestCase.h>
+#include <grp.h>
+
+void check_correctness(struct group* gr);
+
+void check_correctness(struct group* gr)
+{
+    EXPECT_NE(gr, nullptr);
+    EXPECT_EQ(gr->gr_gid, (gid_t)3);
+    EXPECT_EQ(gr->gr_name, "phys"sv);
+    EXPECT_EQ(gr->gr_passwd, "x"sv);
+
+    HashTable<ByteString> members;
+    for (char** mem = gr->gr_mem; *mem; ++mem) {
+        members.set(ByteString(*mem));
+    }
+
+    EXPECT_EQ(true, members.contains("window"sv));
+    EXPECT_EQ(true, members.contains("anon"sv));
+}
+
+TEST_CASE(getgrid_returns_correct_value)
+{
+    // From Base/etc/group
+    // phys:x:3:window,anon
+    struct group* gr = getgrgid(3);
+
+    check_correctness(gr);
+
+    gr = getgrgid(99999);
+    EXPECT_EQ(gr, nullptr);
+}
+
+TEST_CASE(getgrid_r_uses_provided_buffer)
+{
+    // From Base/etc/group
+    // phys:x:3:window,anon
+
+    struct group g;
+    struct group* res;
+    AK::Array<char, 1024> buffer;
+
+    setgrent();
+    int rc = getgrgid_r(3, &g, buffer.data(), buffer.size(), &res);
+    endgrent();
+    EXPECT_EQ(rc, 0);
+    check_correctness(&g);
+    EXPECT_EQ(res, &g);
+
+    auto is_pointer_in_range = [&buffer](void* ptr) {
+        return (buffer.data() <= ptr) && (ptr < buffer.data() + buffer.size());
+    };
+
+    EXPECT(is_pointer_in_range(g.gr_mem));
+    EXPECT(is_pointer_in_range(g.gr_name));
+
+    char** mem = g.gr_mem;
+    for (; *mem; ++mem) {
+        EXPECT(is_pointer_in_range(mem));
+        EXPECT(is_pointer_in_range(*mem));
+    }
+    EXPECT(is_pointer_in_range(mem));
+}
+
+TEST_CASE(getgrname_r_uses_provided_buffer)
+{
+    // From Base/etc/group
+    // phys:x:3:window,anon
+
+    struct group g;
+    struct group* res;
+    AK::Array<char, 1024> buffer;
+    setgrent();
+    int rc = getgrnam_r("phys", &g, buffer.data(), buffer.size(), &res);
+    endgrent();
+    EXPECT_EQ(rc, 0);
+    check_correctness(&g);
+    EXPECT_EQ(res, &g);
+
+    auto is_pointer_in_range = [&buffer](void* ptr) {
+        return (buffer.data() <= ptr) && (ptr < buffer.data() + buffer.size());
+    };
+
+    EXPECT(is_pointer_in_range(g.gr_mem));
+    EXPECT(is_pointer_in_range(g.gr_name));
+
+    char** mem = g.gr_mem;
+    for (; *mem; ++mem) {
+        EXPECT(is_pointer_in_range(mem));
+        EXPECT(is_pointer_in_range(*mem));
+    }
+    EXPECT(is_pointer_in_range(mem));
+}
diff --git a/Userland/Libraries/LibC/grp.cpp b/Userland/Libraries/LibC/grp.cpp
index 8157817d5e..6d9ef042ce 100644
--- a/Userland/Libraries/LibC/grp.cpp
+++ b/Userland/Libraries/LibC/grp.cpp
@@ -6,7 +6,9 @@
  */
 
 #include <AK/Format.h>
+#include <AK/Forward.h>
 #include <AK/ScopeGuard.h>
+#include <AK/StringView.h>
 #include <AK/Vector.h>
 #include <errno.h>
 #include <errno_codes.h>
@@ -53,6 +55,16 @@ struct group* getgrgid(gid_t gid)
     return nullptr;
 }
 
+int getgrgid_r(gid_t gid, struct group* group_buf, char* buffer, size_t buffer_size, struct group** group_entry_ptr)
+{
+    while (0 == getgrent_r(group_buf, buffer, buffer_size, group_entry_ptr)) {
+        if (group_buf->gr_gid == gid) {
+            return 0;
+        }
+    }
+    return ENOENT;
+}
+
 struct group* getgrnam(char const* name)
 {
     setgrent();
@@ -63,6 +75,14 @@ struct group* getgrnam(char const* name)
     }
     return nullptr;
 }
+int getgrnam_r(char const* name, struct group* group_buf, char* buffer, size_t buffer_size, struct group** group_entry_ptr)
+{
+    while (0 == getgrent_r(group_buf, buffer, buffer_size, group_entry_ptr)) {
+        if (!strcmp(group_buf->gr_name, name))
+            return 0;
+    }
+    return ENOENT;
+}
 
 static bool parse_grpdb_entry(char* buffer, size_t buffer_size, struct group& group_entry)
 {
diff --git a/Userland/Libraries/LibC/grp.h b/Userland/Libraries/LibC/grp.h
index a3cbd61b59..f66ad2e2b5 100644
--- a/Userland/Libraries/LibC/grp.h
+++ b/Userland/Libraries/LibC/grp.h
@@ -25,7 +25,9 @@ int getgrent_r(struct group* group_buf, char* buffer, size_t buffer_size, struct
 void setgrent(void);
 void endgrent(void);
 struct group* getgrnam(char const* name);
+int getgrnam_r(char const* name, struct group* group_buf, char* buffer, size_t buffer_size, struct group** group_entry_ptr);
 struct group* getgrgid(gid_t);
+int getgrgid_r(gid_t gid, struct group* group_buf, char* buffer, size_t buffer_size, struct group** group_entry_ptr);
 int putgrent(const struct group*, FILE*);
 
 int initgroups(char const* user, gid_t);