diff --git a/src/rt/sync/lock_and_signal.cpp b/src/rt/sync/lock_and_signal.cpp
index f9d40681a60a..fa19b63385dd 100644
--- a/src/rt/sync/lock_and_signal.cpp
+++ b/src/rt/sync/lock_and_signal.cpp
@@ -19,7 +19,18 @@ lock_and_signal::lock_and_signal()
     : _holding_thread(INVALID_THREAD)
 {
     _event = CreateEvent(NULL, FALSE, FALSE, NULL);
-    InitializeCriticalSection(&_cs);
+
+    // If a CRITICAL_SECTION is not initialized with a spin count, it will
+    // default to 0, even on multi-processor systems. MSDN suggests using
+    // 4000. On single-processor systems, the spin count parameter is ignored
+    // and the critical section's spin count defaults to 0.
+    const DWORD SPIN_COUNT = 4000;
+    CHECKED(!InitializeCriticalSectionAndSpinCount(&_cs, SPIN_COUNT));
+
+    // TODO? Consider checking GetProcAddress("InitializeCriticalSectionEx")
+    // so Windows >= Vista we can use CRITICAL_SECTION_NO_DEBUG_INFO to avoid
+    // allocating CRITICAL_SECTION debug info that is never released. See:
+    // http://stackoverflow.com/questions/804848/critical-sections-leaking-memory-on-vista-win2008#889853
 }
 
 #else
@@ -32,8 +43,10 @@ lock_and_signal::lock_and_signal()
 #endif
 
 lock_and_signal::~lock_and_signal() {
+    assert(_holding_thread == INVALID_THREAD);
 #if defined(__WIN32__)
     CloseHandle(_event);
+    DeleteCriticalSection(&_cs);
 #else
     CHECKED(pthread_cond_destroy(&_cond));
     CHECKED(pthread_mutex_destroy(&_mutex));
@@ -41,6 +54,7 @@ lock_and_signal::~lock_and_signal() {
 }
 
 void lock_and_signal::lock() {
+    assert(!lock_held_by_current_thread());
 #if defined(__WIN32__)
     EnterCriticalSection(&_cs);
     _holding_thread = GetCurrentThreadId();
@@ -51,6 +65,7 @@ void lock_and_signal::lock() {
 }
 
 void lock_and_signal::unlock() {
+    assert(lock_held_by_current_thread());
     _holding_thread = INVALID_THREAD;
 #if defined(__WIN32__)
     LeaveCriticalSection(&_cs);
@@ -69,9 +84,11 @@ void lock_and_signal::wait() {
     LeaveCriticalSection(&_cs);
     WaitForSingleObject(_event, INFINITE);
     EnterCriticalSection(&_cs);
+    assert(_holding_thread == INVALID_THREAD);
     _holding_thread = GetCurrentThreadId();
 #else
     CHECKED(pthread_cond_wait(&_cond, &_mutex));
+    assert(_holding_thread == INVALID_THREAD);
     _holding_thread = pthread_self();
 #endif
 }