diff --git a/osdep/win32/include/pthread.h b/osdep/win32/include/pthread.h
index 7b82eb2651..e1324a0bb0 100644
--- a/osdep/win32/include/pthread.h
+++ b/osdep/win32/include/pthread.h
@@ -25,19 +25,21 @@
 int pthread_once(pthread_once_t *once_control, void (*init_routine)(void));
 
 typedef struct {
-    char static_mutex;
-    INIT_ONCE static_init;
-    CRITICAL_SECTION cs;
+    char use_cs;
+    union {
+        SRWLOCK srw;
+        CRITICAL_SECTION cs;
+    } lock;
 } pthread_mutex_t;
 
-#define PTHREAD_MUTEX_INITIALIZER {1, INIT_ONCE_STATIC_INIT}
+// Assume SRWLOCK_INIT is {0} so we can easily remain C89-compatible.
+#define PTHREAD_MUTEX_INITIALIZER {0}
 
 #define pthread_mutexattr_t int
 #define pthread_mutexattr_destroy(attr) (void)0
 #define pthread_mutexattr_init(attr) (*(attr) = 0)
-#define pthread_mutexattr_settype(attr, type) (void)0
-// CRITICAL_SECTION is always recursive
-#define PTHREAD_MUTEX_RECURSIVE 0
+#define pthread_mutexattr_settype(attr, type) (*(attr) = (type))
+#define PTHREAD_MUTEX_RECURSIVE 1
 
 int pthread_mutex_destroy(pthread_mutex_t *mutex);
 int pthread_mutex_init(pthread_mutex_t *restrict mutex,
diff --git a/osdep/win32/pthread.c b/osdep/win32/pthread.c
index 4838df48b7..b215e46ba2 100644
--- a/osdep/win32/pthread.c
+++ b/osdep/win32/pthread.c
@@ -32,35 +32,40 @@ int pthread_once(pthread_once_t *once_control, void (*init_routine)(void))
 
 int pthread_mutex_destroy(pthread_mutex_t *mutex)
 {
-    DeleteCriticalSection(&mutex->cs);
+    if (mutex->use_cs)
+        DeleteCriticalSection(&mutex->lock.cs);
     return 0;
 }
 
 int pthread_mutex_init(pthread_mutex_t *restrict mutex,
                        const pthread_mutexattr_t *restrict attr)
 {
-    InitializeCriticalSection(&mutex->cs);
+    mutex->use_cs = attr && (*attr & PTHREAD_MUTEX_RECURSIVE);
+    if (mutex->use_cs) {
+        InitializeCriticalSection(&mutex->lock.cs);
+    } else {
+        InitializeSRWLock(&mutex->lock.srw);
+    }
     return 0;
 }
 
 int pthread_mutex_lock(pthread_mutex_t *mutex)
 {
-    if (mutex->static_mutex) {
-        BOOL pending;
-        if (!InitOnceBeginInitialize(&mutex->static_init, 0, &pending, NULL))
-            abort();
-        if (pending) {
-            InitializeCriticalSection(&mutex->cs);
-            InitOnceComplete(&mutex->static_init, 0, NULL);
-        }
+    if (mutex->use_cs) {
+        EnterCriticalSection(&mutex->lock.cs);
+    } else {
+        AcquireSRWLockExclusive(&mutex->lock.srw);
     }
-    EnterCriticalSection(&mutex->cs);
     return 0;
 }
 
 int pthread_mutex_unlock(pthread_mutex_t *mutex)
 {
-    LeaveCriticalSection(&mutex->cs);
+    if (mutex->use_cs) {
+        LeaveCriticalSection(&mutex->lock.cs);
+    } else {
+        ReleaseSRWLockExclusive(&mutex->lock.srw);
+    }
     return 0;
 }
 
@@ -68,7 +73,13 @@ static int cond_wait(pthread_cond_t *restrict cond,
                      pthread_mutex_t *restrict mutex,
                      DWORD ms)
 {
-    return SleepConditionVariableCS(cond, &mutex->cs, ms) ? 0 : ETIMEDOUT;
+    BOOL res;
+    if (mutex->use_cs) {
+        res = SleepConditionVariableCS(cond, &mutex->lock.cs, ms);
+    } else {
+        res = SleepConditionVariableSRW(cond, &mutex->lock.srw, ms, 0);
+    }
+    return res ? 0 : ETIMEDOUT;
 }
 
 int pthread_cond_timedwait(pthread_cond_t *restrict cond,