Index: src/mutex.c
==================================================================
--- src/mutex.c
+++ src/mutex.c
@@ -65,10 +65,11 @@
       pFrom = sqlite3NoopMutex();
     }
     mutexCopy(&sqlite3GlobalConfig.mutex, pFrom);
     sqlite3MemoryBarrier();
   }
+  assert( sqlite3GlobalConfig.mutex.xMutexInit );
   rc = sqlite3GlobalConfig.mutex.xMutexInit();
 
 #ifdef SQLITE_DEBUG
   GLOBAL(int, mutexIsInit) = 1;
 #endif
@@ -99,26 +100,29 @@
 sqlite3_mutex *sqlite3_mutex_alloc(int id){
 #ifndef SQLITE_OMIT_AUTOINIT
   if( id<=SQLITE_MUTEX_RECURSIVE && sqlite3_initialize() ) return 0;
   if( id>SQLITE_MUTEX_RECURSIVE && sqlite3MutexInit() ) return 0;
 #endif
+  assert( sqlite3GlobalConfig.mutex.xMutexAlloc );
   return sqlite3GlobalConfig.mutex.xMutexAlloc(id);
 }
 
 sqlite3_mutex *sqlite3MutexAlloc(int id){
   if( !sqlite3GlobalConfig.bCoreMutex ){
     return 0;
   }
   assert( GLOBAL(int, mutexIsInit) );
+  assert( sqlite3GlobalConfig.mutex.xMutexAlloc );
   return sqlite3GlobalConfig.mutex.xMutexAlloc(id);
 }
 
 /*
 ** Free a dynamic mutex.
 */
 void sqlite3_mutex_free(sqlite3_mutex *p){
   if( p ){
+    assert( sqlite3GlobalConfig.mutex.xMutexFree );
     sqlite3GlobalConfig.mutex.xMutexFree(p);
   }
 }
 
 /*
@@ -125,10 +129,11 @@
 ** Obtain the mutex p. If some other thread already has the mutex, block
 ** until it can be obtained.
 */
 void sqlite3_mutex_enter(sqlite3_mutex *p){
   if( p ){
+    assert( sqlite3GlobalConfig.mutex.xMutexEnter );
     sqlite3GlobalConfig.mutex.xMutexEnter(p);
   }
 }
 
 /*
@@ -136,10 +141,11 @@
 ** thread holds the mutex and it cannot be obtained, return SQLITE_BUSY.
 */
 int sqlite3_mutex_try(sqlite3_mutex *p){
   int rc = SQLITE_OK;
   if( p ){
+    assert( sqlite3GlobalConfig.mutex.xMutexTry );
     return sqlite3GlobalConfig.mutex.xMutexTry(p);
   }
   return rc;
 }
 
@@ -149,10 +155,11 @@
 ** is not currently entered. If a NULL pointer is passed as an argument
 ** this function is a no-op.
 */
 void sqlite3_mutex_leave(sqlite3_mutex *p){
   if( p ){
+    assert( sqlite3GlobalConfig.mutex.xMutexLeave );
     sqlite3GlobalConfig.mutex.xMutexLeave(p);
   }
 }
 
 #ifndef NDEBUG
@@ -159,13 +166,15 @@
 /*
 ** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
 ** intended for use inside assert() statements.
 */
 int sqlite3_mutex_held(sqlite3_mutex *p){
+  assert( p==0 || sqlite3GlobalConfig.mutex.xMutexHeld );
   return p==0 || sqlite3GlobalConfig.mutex.xMutexHeld(p);
 }
 int sqlite3_mutex_notheld(sqlite3_mutex *p){
+  assert( p==0 || sqlite3GlobalConfig.mutex.xMutexNotheld );
   return p==0 || sqlite3GlobalConfig.mutex.xMutexNotheld(p);
 }
 #endif
 
 #endif /* !defined(SQLITE_MUTEX_OMIT) */