diff --git a/winsup/cygwin/fhandler_timerfd.cc b/winsup/cygwin/fhandler_timerfd.cc
index 8a6c4b559..2a0521708 100644
--- a/winsup/cygwin/fhandler_timerfd.cc
+++ b/winsup/cygwin/fhandler_timerfd.cc
@@ -187,6 +187,35 @@ fhandler_timerfd::dup (fhandler_base *child, int flags)
   return ret;
 }
 
+int
+fhandler_timerfd::ioctl (unsigned int cmd, void *p)
+{
+  int ret = -1;
+  uint64_t exp_cnt;
+
+  switch (cmd)
+    {
+    case TFD_IOC_SET_TICKS:
+      __try
+	{
+	  timerfd_tracker *tfd = (timerfd_tracker *) timerid;
+
+	  exp_cnt = *(uint64_t *) p;
+	  ret = tfd->ioctl_set_ticks (exp_cnt);
+	  if (ret < 0)
+	    set_errno (-ret);
+	}
+      __except (EFAULT) {}
+      __endtry
+      break;
+    default:
+      ret = fhandler_base::ioctl (cmd, p);
+      break;
+    }
+  syscall_printf ("%d = ioctl_timerfd(%x, %p)", ret, cmd, p);
+  return ret;
+}
+
 void
 fhandler_timerfd::fixup_after_fork (HANDLE)
 {
@@ -214,39 +243,6 @@ fhandler_timerfd::fixup_after_exec ()
   __endtry
 }
 
-int
-fhandler_timerfd::ioctl (unsigned int cmd, void *p)
-{
-  int ret = -1;
-  uint64_t exp_cnt;
-
-  switch (cmd)
-    {
-    case TFD_IOC_SET_TICKS:
-      __try
-	{
-	  timerfd_tracker *tfd = (timerfd_tracker *) timerid;
-
-	  exp_cnt = *(uint64_t *) p;
-	  if (!exp_cnt)
-	    {
-	      set_errno (EINVAL);
-	      break;
-	    }
-	  tfd->ioctl_set_ticks (exp_cnt);
-	  ret = 0;
-	}
-      __except (EFAULT) {}
-      __endtry
-      break;
-    default:
-      ret = fhandler_base::ioctl (cmd, p);
-      break;
-    }
-  syscall_printf ("%d = ioctl_timerfd(%x, %p)", ret, cmd, p);
-  return ret;
-}
-
 fhandler_timerfd::~fhandler_timerfd ()
 {
   __try
diff --git a/winsup/cygwin/timerfd.cc b/winsup/cygwin/timerfd.cc
index 08fff312c..a03749a60 100644
--- a/winsup/cygwin/timerfd.cc
+++ b/winsup/cygwin/timerfd.cc
@@ -394,11 +394,18 @@ timerfd_tracker::close ()
   InterlockedDecrement (&tfd_shared->instance_count);
 }
 
-void
-timerfd_tracker::ioctl_set_ticks (uint64_t exp_cnt)
+int
+timerfd_tracker::ioctl_set_ticks (uint64_t new_exp_cnt)
 {
+  LONG64 exp_cnt = (LONG64) new_exp_cnt;
+  if (exp_cnt == 0 || exp_cnt == -1LL)
+    return -EINVAL;
+  if (!enter_critical_section ())
+    return -EBADF;
   set_expiration_count (exp_cnt);
   timer_expired ();
+  leave_critical_section ();
+  return 0;
 }
 
 void
diff --git a/winsup/cygwin/timerfd.h b/winsup/cygwin/timerfd.h
index 1f9f76268..66bf78424 100644
--- a/winsup/cygwin/timerfd.h
+++ b/winsup/cygwin/timerfd.h
@@ -148,7 +148,7 @@ class timerfd_tracker		/* cygheap! */
   int settime (int, const struct itimerspec *, struct itimerspec *);
   static void dtor (timerfd_tracker *);
   void close ();
-  void ioctl_set_ticks (uint64_t);
+  int ioctl_set_ticks (uint64_t);
   void fixup_after_fork_exec (bool);
   void fixup_after_fork () { fixup_after_fork_exec (false); }
   void fixup_after_exec () { fixup_after_fork_exec (true); }