diff --git a/libc/bionic/pthread_create.cpp b/libc/bionic/pthread_create.cpp
index bfa4e8c..ab92853 100644
--- a/libc/bionic/pthread_create.cpp
+++ b/libc/bionic/pthread_create.cpp
@@ -41,7 +41,6 @@
 #include "private/bionic_tls.h"
 #include "private/libc_logging.h"
 #include "private/ErrnoRestorer.h"
-#include "private/ScopedPthreadMutexLocker.h"
 
 // x86 uses segment descriptors rather than a direct pointer to TLS.
 #if defined(__i386__)
diff --git a/libc/bionic/pthread_getcpuclockid.cpp b/libc/bionic/pthread_getcpuclockid.cpp
index 2bf2004..f641e4c 100644
--- a/libc/bionic/pthread_getcpuclockid.cpp
+++ b/libc/bionic/pthread_getcpuclockid.cpp
@@ -31,13 +31,11 @@
 #include "pthread_internal.h"
 
 int pthread_getcpuclockid(pthread_t t, clockid_t* clockid) {
-  pthread_internal_t* thread = __pthread_internal_find(t);
-  if (thread == NULL) {
-    return ESRCH;
-  }
+  pid_t tid = pthread_gettid_np(t);
+  if (tid == -1) return ESRCH;
 
   // The tid is stored in the top bits, but negated.
-  clockid_t result = ~static_cast<clockid_t>(thread->tid) << 3;
+  clockid_t result = ~static_cast<clockid_t>(tid) << 3;
   // Bits 0 and 1: clock type (0 = CPUCLOCK_PROF, 1 = CPUCLOCK_VIRT, 2 = CPUCLOCK_SCHED).
   result |= 2;
   // Bit 2: thread (set) or process (clear)?
diff --git a/libc/bionic/pthread_getschedparam.cpp b/libc/bionic/pthread_getschedparam.cpp
index 052fb05..cc1ece8 100644
--- a/libc/bionic/pthread_getschedparam.cpp
+++ b/libc/bionic/pthread_getschedparam.cpp
@@ -34,15 +34,10 @@
 int pthread_getschedparam(pthread_t t, int* policy, sched_param* param) {
   ErrnoRestorer errno_restorer;
 
-  pthread_internal_t* thread = __pthread_internal_find(t);
-  if (thread == NULL) {
-    return ESRCH;
-  }
+  pid_t tid = pthread_gettid_np(t);
+  if (tid == -1) return ESRCH;
 
-  int rc = sched_getparam(thread->tid, param);
-  if (rc == -1) {
-    return errno;
-  }
-  *policy = sched_getscheduler(thread->tid);
+  if (sched_getparam(tid, param) == -1) return errno;
+  *policy = sched_getscheduler(tid);
   return 0;
 }
diff --git a/libc/bionic/pthread_gettid_np.cpp b/libc/bionic/pthread_gettid_np.cpp
index c996a05..fe85442 100644
--- a/libc/bionic/pthread_gettid_np.cpp
+++ b/libc/bionic/pthread_gettid_np.cpp
@@ -29,5 +29,6 @@
 #include "pthread_internal.h"
 
 pid_t pthread_gettid_np(pthread_t t) {
-  return reinterpret_cast<pthread_internal_t*>(t)->tid;
+  pthread_internal_t* thread = __pthread_internal_find(t);
+  return thread ? thread->tid : -1;
 }
diff --git a/libc/bionic/pthread_internal.cpp b/libc/bionic/pthread_internal.cpp
index 8946f79..51430e7 100644
--- a/libc/bionic/pthread_internal.cpp
+++ b/libc/bionic/pthread_internal.cpp
@@ -34,20 +34,38 @@
 #include <sys/mman.h>
 
 #include "private/bionic_futex.h"
+#include "private/bionic_sdk_version.h"
 #include "private/bionic_tls.h"
 #include "private/libc_logging.h"
-#include "private/ScopedPthreadMutexLocker.h"
 
-static pthread_internal_t* g_thread_list = NULL;
-static pthread_mutex_t g_thread_list_lock = PTHREAD_MUTEX_INITIALIZER;
+static pthread_internal_t* g_thread_list = nullptr;
+static pthread_rwlock_t g_thread_list_lock = PTHREAD_RWLOCK_INITIALIZER;
+
+template <bool write> class ScopedRWLock {
+ public:
+  ScopedRWLock(pthread_rwlock_t* rwlock) : rwlock_(rwlock) {
+    (write ? pthread_rwlock_wrlock : pthread_rwlock_rdlock)(rwlock_);
+  }
+
+  ~ScopedRWLock() {
+    pthread_rwlock_unlock(rwlock_);
+  }
+
+ private:
+  pthread_rwlock_t* rwlock_;
+  DISALLOW_IMPLICIT_CONSTRUCTORS(ScopedRWLock);
+};
+
+typedef ScopedRWLock<true> ScopedWriteLock;
+typedef ScopedRWLock<false> ScopedReadLock;
 
 pthread_t __pthread_internal_add(pthread_internal_t* thread) {
-  ScopedPthreadMutexLocker locker(&g_thread_list_lock);
+  ScopedWriteLock locker(&g_thread_list_lock);
 
   // We insert at the head.
   thread->next = g_thread_list;
-  thread->prev = NULL;
-  if (thread->next != NULL) {
+  thread->prev = nullptr;
+  if (thread->next != nullptr) {
     thread->next->prev = thread;
   }
   g_thread_list = thread;
@@ -55,12 +73,12 @@
 }
 
 void __pthread_internal_remove(pthread_internal_t* thread) {
-  ScopedPthreadMutexLocker locker(&g_thread_list_lock);
+  ScopedWriteLock locker(&g_thread_list_lock);
 
-  if (thread->next != NULL) {
+  if (thread->next != nullptr) {
     thread->next->prev = thread->prev;
   }
-  if (thread->prev != NULL) {
+  if (thread->prev != nullptr) {
     thread->prev->next = thread->next;
   } else {
     g_thread_list = thread->next;
@@ -82,17 +100,17 @@
 pthread_internal_t* __pthread_internal_find(pthread_t thread_id) {
   pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(thread_id);
 
-  // check if thread is pthread_self() before acquiring the lock
-  if (thread == __get_thread()) {
-    return thread;
+  // Check if we're looking for ourselves before acquiring the lock.
+  if (thread == __get_thread()) return thread;
+
+  ScopedReadLock locker(&g_thread_list_lock);
+  for (pthread_internal_t* t = g_thread_list; t != nullptr; t = t->next) {
+    if (t == thread) return thread;
   }
 
-  ScopedPthreadMutexLocker locker(&g_thread_list_lock);
-
-  for (pthread_internal_t* t = g_thread_list; t != NULL; t = t->next) {
-    if (t == thread) {
-      return thread;
-    }
+  // Historically we'd return null, but
+  if (bionic_get_application_target_sdk_version() >= __ANDROID_API_O__) {
+    __libc_fatal("attempt to use invalid pthread_t");
   }
-  return NULL;
+  return nullptr;
 }
diff --git a/libc/bionic/pthread_kill.cpp b/libc/bionic/pthread_kill.cpp
index 72a6ed1..3761a75 100644
--- a/libc/bionic/pthread_kill.cpp
+++ b/libc/bionic/pthread_kill.cpp
@@ -35,10 +35,8 @@
 int pthread_kill(pthread_t t, int sig) {
   ErrnoRestorer errno_restorer;
 
-  pthread_internal_t* thread = __pthread_internal_find(t);
-  if (thread == NULL) {
-    return ESRCH;
-  }
+  pid_t tid = pthread_gettid_np(t);
+  if (tid == -1) return ESRCH;
 
-  return (tgkill(getpid(), thread->tid, sig) == -1) ? errno : 0;
+  return (tgkill(getpid(), tid, sig) == -1) ? errno : 0;
 }
diff --git a/libc/bionic/pthread_setname_np.cpp b/libc/bionic/pthread_setname_np.cpp
index 6d2880e..f582d53 100644
--- a/libc/bionic/pthread_setname_np.cpp
+++ b/libc/bionic/pthread_setname_np.cpp
@@ -43,14 +43,8 @@
 #define MAX_TASK_COMM_LEN 16
 
 static int __open_task_comm_fd(pthread_t t, int flags) {
-  pthread_internal_t* thread = __pthread_internal_find(t);
-  if (thread == nullptr) {
-    errno = ENOENT;
-    return -1;
-  }
-
   char comm_name[64];
-  snprintf(comm_name, sizeof(comm_name), "/proc/self/task/%d/comm", thread->tid);
+  snprintf(comm_name, sizeof(comm_name), "/proc/self/task/%d/comm", pthread_gettid_np(t));
   return open(comm_name, O_CLOEXEC | flags);
 }
 
diff --git a/libc/bionic/pthread_setschedparam.cpp b/libc/bionic/pthread_setschedparam.cpp
index 0ad68bb..3e80959 100644
--- a/libc/bionic/pthread_setschedparam.cpp
+++ b/libc/bionic/pthread_setschedparam.cpp
@@ -34,14 +34,8 @@
 int pthread_setschedparam(pthread_t t, int policy, const sched_param* param) {
   ErrnoRestorer errno_restorer;
 
-  pthread_internal_t* thread = __pthread_internal_find(t);
-  if (thread == NULL) {
-    return ESRCH;
-  }
+  pid_t tid = pthread_gettid_np(t);
+  if (tid == -1) return ESRCH;
 
-  int rc = sched_setscheduler(thread->tid, policy, param);
-  if (rc == -1) {
-    return errno;
-  }
-  return 0;
+  return (sched_setscheduler(tid, policy, param) == -1) ? errno : 0;
 }