diff --git a/ntp_signd.c b/ntp_signd.c
index 0d88d7b..6328b61 100644
--- a/ntp_signd.c
+++ b/ntp_signd.c
@@ -235,7 +235,7 @@ read_write_socket(int sock_fd, int event, void *anything)
       return;
 
     /* Disable output and wait for a response */
-    SCH_SetFileHandlerEvents(sock_fd, SCH_FILE_INPUT);
+    SCH_SetFileHandlerEvent(sock_fd, SCH_FILE_OUTPUT, 0);
   }
 
   if (event == SCH_FILE_INPUT) {
@@ -283,7 +283,7 @@ read_write_socket(int sock_fd, int event, void *anything)
     /* Move the head and enable output for the next packet */
     queue_head = NEXT_QUEUE_INDEX(queue_head);
     if (!IS_QUEUE_EMPTY())
-      SCH_SetFileHandlerEvents(sock_fd, SCH_FILE_INPUT | SCH_FILE_OUTPUT);
+      SCH_SetFileHandlerEvent(sock_fd, SCH_FILE_OUTPUT, 1);
   }
 }
 
@@ -369,7 +369,7 @@ NSD_SignAndSendPacket(uint32_t key_id, NTP_Packet *packet, NTP_Remote_Address *r
 
   /* Enable output if there was no pending request */
   if (IS_QUEUE_EMPTY())
-    SCH_SetFileHandlerEvents(sock_fd, SCH_FILE_INPUT | SCH_FILE_OUTPUT);
+    SCH_SetFileHandlerEvent(sock_fd, SCH_FILE_OUTPUT, 1);
 
   queue_tail = NEXT_QUEUE_INDEX(queue_tail);
 
diff --git a/sched.c b/sched.c
index 21b55a7..45ef11c 100644
--- a/sched.c
+++ b/sched.c
@@ -219,13 +219,16 @@ SCH_RemoveFileHandler(int fd)
 /* ================================================== */
 
 void
-SCH_SetFileHandlerEvents(int fd, int events)
+SCH_SetFileHandlerEvent(int fd, int event, int enable)
 {
   FileHandlerEntry *ptr;
 
-  assert(events);
   ptr = ARR_GetElement(file_handlers, fd);
-  ptr->events = events;
+
+  if (enable)
+    ptr->events |= event;
+  else
+    ptr->events &= ~event;
 }
 
 /* ================================================== */
diff --git a/sched.h b/sched.h
index bfb6169..5ff53c7 100644
--- a/sched.h
+++ b/sched.h
@@ -60,7 +60,7 @@ extern void SCH_Finalise(void);
 /* Register a handler for when select goes true on a file descriptor */
 extern void SCH_AddFileHandler(int fd, int events, SCH_FileHandler handler, SCH_ArbitraryArgument arg);
 extern void SCH_RemoveFileHandler(int fd);
-extern void SCH_SetFileHandlerEvents(int fd, int events);
+extern void SCH_SetFileHandlerEvent(int fd, int event, int enable);
 
 /* Get the time stamp taken after a file descriptor became ready or a timeout expired */
 extern void SCH_GetLastEventTime(struct timespec *cooked, double *err, struct timespec *raw);