diff --git a/libc/test/integration/src/pthread/CMakeLists.txt b/libc/test/integration/src/pthread/CMakeLists.txt
--- a/libc/test/integration/src/pthread/CMakeLists.txt
+++ b/libc/test/integration/src/pthread/CMakeLists.txt
@@ -129,6 +129,13 @@
     libc.include.stdio
     libc.src.pthread.pthread_create
     libc.src.pthread.pthread_join
+    libc.src.pthread.pthread_attr_setdetachstate
+    libc.src.pthread.pthread_attr_init
+    libc.src.pthread.pthread_attr_destroy
+    libc.src.stdlib.srand
+    libc.src.stdlib.rand
+    libc.src.__support.CPP.atomic
+    libc.src.__support.CPP.new
 )
 
 add_integration_test(
diff --git a/libc/test/integration/src/pthread/pthread_join_test.cpp b/libc/test/integration/src/pthread/pthread_join_test.cpp
--- a/libc/test/integration/src/pthread/pthread_join_test.cpp
+++ b/libc/test/integration/src/pthread/pthread_join_test.cpp
@@ -1,4 +1,4 @@
-//===-- Tests for pthread_join-- ------------------------------------------===//
+//===-- Tests for pthread_join --------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,15 +6,105 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "src/pthread/pthread_attr_destroy.h"
+#include "src/pthread/pthread_attr_init.h"
+#include "src/pthread/pthread_attr_setdetachstate.h"
 #include "src/pthread/pthread_create.h"
 #include "src/pthread/pthread_join.h"
 
+#include "src/stdlib/rand.h"
+#include "src/stdlib/srand.h"
+
+#include "src/__support/CPP/atomic.h"
+#include "src/__support/CPP/new.h"
+
+#include "src/__support/threads/thread.h"
 #include "src/errno/libc_errno.h"
 
 #include "test/IntegrationTest/test.h"
+
+#include <linux/param.h> // For EXEC_PAGESIZE.
 #include <pthread.h>
 
+struct TestThreadArgs {
+  pthread_t Tid;
+  int Detached;
+  volatile int Done;
+  size_t SpinCnt;
+  void *Ret;
+};
+static __llvm_libc::AllocChecker AC;
+
+static void *func(void *Arg) {
+  TestThreadArgs *ThArg = reinterpret_cast<TestThreadArgs *>(Arg);
+  volatile size_t SpinCnt = ThArg->SpinCnt;
+
+  while (SpinCnt) {
+    --SpinCnt;
+  }
+
+  ThArg->Done = 1;
+  return ThArg->Ret;
+}
+
 static void *simpleFunc(void *) { return nullptr; }
+
+static TestThreadArgs *initializeTestThreadArgs(size_t NumThreads,
+                                                unsigned detached_percent) {
+  TestThreadArgs *ThArgs = new (AC) TestThreadArgs[NumThreads];
+  for (size_t I = 0; I < NumThreads; ++I) {
+    unsigned RandVal = __llvm_libc::rand();
+    uintptr_t RandRet = __llvm_libc::rand();
+    RandRet *= __llvm_libc::rand();
+    RandVal %= 100;
+    ThArgs[I].Detached = detached_percent > RandVal;
+    ThArgs[I].Done = 0;
+    ThArgs[I].SpinCnt = RandVal % (1000 * 1000);
+    ThArgs[I].Ret = reinterpret_cast<void *>(RandRet);
+  }
+
+  pthread_attr_t Attr;
+  ASSERT_EQ(__llvm_libc::pthread_attr_init(&Attr), 0);
+  for (size_t I = 0; I < NumThreads; ++I) {
+    ASSERT_EQ(__llvm_libc::pthread_attr_setdetachstate(
+                  &Attr, ThArgs[I].Detached ? PTHREAD_CREATE_DETACHED
+                                            : PTHREAD_CREATE_JOINABLE),
+              0);
+
+    ASSERT_EQ(__llvm_libc::pthread_create(&ThArgs[I].Tid, &Attr, func,
+                                          reinterpret_cast<void *>(ThArgs + I)),
+              0);
+  }
+  return ThArgs;
+}
+
+static void runJoinTests(size_t NumThreads, bool JoinAsCompleted) {
+  TestThreadArgs *ThArgs = initializeTestThreadArgs(NumThreads, 0);
+  for (size_t JoinCnt = 0; JoinCnt < NumThreads;) {
+    for (size_t I = 0; I < NumThreads; ++I) {
+      if (ThArgs[I].Detached) {
+        if (ThArgs[I].Done == 1) {
+          ThArgs[I].Done = 2;
+          ++JoinCnt;
+        }
+      } else {
+        if (!JoinAsCompleted || ThArgs[I].Done == 1) {
+          void *ThRet;
+          ASSERT_EQ(__llvm_libc::pthread_join(ThArgs[I].Tid, &ThRet), 0);
+          ASSERT_EQ(libc_errno, 0);
+
+          ASSERT_EQ(ThArgs[I].Done, 1);
+          ASSERT_EQ(ThRet, ThArgs[I].Ret);
+
+          ThArgs[I].Done = 2;
+          ++JoinCnt;
+        }
+      }
+    }
+  }
+  delete ThArgs;
+}
+
 static void nullJoinTest() {
   pthread_t Tid;
   ASSERT_EQ(__llvm_libc::pthread_create(&Tid, nullptr, simpleFunc, nullptr), 0);
@@ -25,6 +115,14 @@
 
 TEST_MAIN() {
   libc_errno = 0;
+  __llvm_libc::srand(123);
+
   nullJoinTest();
+
+  for (size_t NumThreads = 1; NumThreads < 8; ++NumThreads) {
+    runJoinTests(NumThreads, /*JoinAsCompleted*/ true);
+    runJoinTests(NumThreads, /*JoinAsCompleted*/ false);
+  }
+
   return 0;
 }