diff --git a/nwatch.c b/nwatch.c
index bf024ccc..c9a3a83b 100644
--- a/nwatch.c
+++ b/nwatch.c
@@ -81,6 +81,7 @@ static int NetWatchTimerInsQue(pNetWatch self, pNWTimer handle)
   if (self->tq_head == NULL) {
     self->tq_head = self->tq_tail = handle;
     handle->next = NULL;
+    handle->vrfy = NWMAGIC;
     return 1;
   }
   /* if new one is not earlier than latest one, insert after latest */
@@ -90,6 +91,7 @@ static int NetWatchTimerInsQue(pNetWatch self, pNWTimer handle)
     self->tq_tail->next = handle;
     self->tq_tail = handle;
     handle->next = NULL;
+    handle->vrfy = NWMAGIC;
     return 1;
   }
   /* if new one is not later than earliest one, insert before earliest */
@@ -98,6 +100,7 @@ static int NetWatchTimerInsQue(pNetWatch self, pNWTimer handle)
        handle->tv.tv_usec <= self->tq_head->tv.tv_usec)) {
     handle->next = self->tq_head;
     self->tq_head = handle;
+    handle->vrfy = NWMAGIC;
     return 1;
   }
   else
@@ -113,8 +116,10 @@ static int NetWatchTimerInsQue(pNetWatch self, pNWTimer handle)
     /* slip new one in between this one and the next one */
     handle->next = pNxt->next;
     pNxt->next = handle ;
+    handle->vrfy = NWMAGIC;
+    return 1;
   }
-  return 1;
+  return 0;
 }
 
 /*
@@ -125,6 +130,7 @@ static int NetWatchTimerInsQue(pNetWatch self, pNWTimer handle)
  */
 static int NetWatchTimerRemQue(pNetWatch self, pNWTimer handle)
 {
+  assert(handle->vrfy == NWMAGIC);
   /* handle the case of first and possibly only */
   if (handle == self->tq_head) {
     self->tq_head = self->tq_head->next;  /* may be NULL */
@@ -145,12 +151,14 @@ static int NetWatchTimerRemQue(pNetWatch self, pNWTimer handle)
     if (handle == self->tq_tail)
       self->tq_tail = pNxt;
   }
+  handle->vrfy = 0;
   return 1;
 }
 
 int NetWatchRegisterTimer(pNWTimer* handle, int mSec,
     pNWCallback callback, void* context)
 {
+  assert(callback);
   pNetWatch self = instance;
   if(!self || self->lMagic != NWMAGIC)
     return 0;
@@ -168,7 +176,6 @@ int NetWatchRegisterTimer(pNWTimer* handle, int mSec,
   pNew->tick = 0;
   pNew->func = callback;
   pNew->cntx = context;
-  pNew->vrfy = NWMAGIC;
   NetWatchTimerInsQue(self, pNew);
   *handle = pNew;
   return 1;
@@ -177,6 +184,7 @@ int NetWatchRegisterTimer(pNWTimer* handle, int mSec,
 int NetWatchRegisterTimerPeriodic(pNWTimer* handle, int mSecInitial, int mSecPeriod,
     pNWCallback callback, void* context)
 {
+  assert(callback);
   if (NetWatchRegisterTimer(handle, mSecInitial, callback, context)) {
     pNWTimer pNew = *handle;
     if (pNew == NULL)
@@ -208,8 +216,9 @@ int NetWatchRemoveTimer(pNWTimer handle)
   pNetWatch self = instance;
   if (!self || self->lMagic != NWMAGIC)\
     return 0;
+  if (handle == NULL || handle->vrfy != NWMAGIC)
+    return 0;
   NetWatchTimerRemQue(self, handle);
-  handle->vrfy = 0;
   free(handle);
   return 1;
 }
@@ -238,6 +247,7 @@ static int NetWatchContextInsQue(pNetWatch self, pNWContext handle)
     self->cq_tail->next = handle;
     self->cq_tail = handle;
   }
+  handle->vrfy = NWMAGIC;
   return 1;
 }
 
@@ -266,6 +276,7 @@ static void NetWatchContextRemQue(pNetWatch self, pNWContext handle)
     if (handle == self->cq_tail) /* if last */
       self->cq_tail = pNxt;
   }
+  handle->vrfy = 0;
   return;
 }
 
@@ -286,19 +297,19 @@ static void NetWatchContextPrgQue(pNetWatch self)
     free(tmp);
   }
   pNxt = self->cq_head;
-  while (pNxt) {
-    if (pNxt->next && pNxt->next->sock < 0) {
+  while (pNxt && pNxt->next) {
+    if (pNxt->next->sock < 0) {
       pNWContext tmp = NULL;
       tmp = pNxt->next;
       pNxt->next = pNxt->next->next;
       tmp->vrfy = 0;
       free(tmp);
+      continue;
     }
     pNxt = pNxt->next;
   }
-  /* if the queue is empty clear the tail */
-  if (self->cq_head == NULL)
-    self->cq_tail = pNxt;
+  /* if the queue is empty then pNxt is NULL else pNxt points to the tail */
+  self->cq_tail = pNxt;
   self->nInvalid = 0;
   return;
 }
@@ -306,6 +317,7 @@ static void NetWatchContextPrgQue(pNetWatch self)
 int NetWatchRegisterCallback(pNWContext* handle, int iSocket,
     pNWCallback callback, void* context)
 {
+  assert(callback);
   pNWContext pNew = NULL;
   pNetWatch self = instance;
   if(!self || self->lMagic != NWMAGIC)
@@ -320,7 +332,6 @@ int NetWatchRegisterCallback(pNWContext* handle, int iSocket,
   pNew->mode = nwatch_read;
   pNew->func = callback;
   pNew->cntx = context;
-  pNew->vrfy = NWMAGIC;
   *handle = pNew;
   NetWatchContextInsQue(self, pNew);
   return 1;
@@ -375,7 +386,7 @@ int NetWatchTask (void* pData)
   if (self->nInvalid > 0)
     NetWatchContextPrgQue(self);
 
-  /* build the select  mask */
+  /* build the select mask */
   FD_ZERO(&rMask);
   FD_ZERO(&wMask);
   pNWC = self->cq_head;
@@ -453,7 +464,6 @@ int NetWatchTask (void* pData)
         NetWatchTimerInsQue(self, pNew);
       }
       else {
-        pNew->vrfy = 0;
         free(pNew);
       }
     }