diff --git a/fhem/CHANGED b/fhem/CHANGED
index 7fe58def6..c880b5ccd 100644
--- a/fhem/CHANGED
+++ b/fhem/CHANGED
@@ -463,3 +463,4 @@
   - feature: contrib/fhem2speech from Martin
   - bugfix:  attributes of at devices disappear
   - feature: attribute rainadjustment for KS300 (Boris 2008-12-17)
+  - bugfix:  deleting at / watchdog while active creates an empty device
diff --git a/fhem/FHEM/90_at.pm b/fhem/FHEM/90_at.pm
index e2cebd111..c36f330a0 100755
--- a/fhem/FHEM/90_at.pm
+++ b/fhem/FHEM/90_at.pm
@@ -12,6 +12,7 @@ at_Initialize($)
   my ($hash) = @_;
 
   $hash->{DefFn}    = "at_Define";
+  $hash->{UndefFn}  = "at_Undef";
   $hash->{AttrFn}   = "at_Attr";
   $hash->{AttrList} = "disable:0,1 skip_next:0,1";
 }
@@ -75,6 +76,14 @@ at_Define($$)
   return undef;
 }
 
+sub
+at_Undef($$)
+{
+  my ($hash, $name) = @_;
+  RemoveInternalTimer($name);
+  return undef;
+}
+
 sub
 at_Exec($)
 {
diff --git a/fhem/FHEM/91_watchdog.pm b/fhem/FHEM/91_watchdog.pm
index 2c3dab903..4af6753f4 100755
--- a/fhem/FHEM/91_watchdog.pm
+++ b/fhem/FHEM/91_watchdog.pm
@@ -12,6 +12,7 @@ watchdog_Initialize($)
   my ($hash) = @_;
 
   $hash->{DefFn} = "watchdog_Define";
+  $hash->{UndefFn} = "watchdog_Undef";
   $hash->{NotifyFn} = "watchdog_Notify";
   $hash->{AttrList} = "disable:0,1";
 }
@@ -108,5 +109,13 @@ watchdog_Activate($)
   InternalTimer($nt, "watchdog_Trigger", $ntfy, 0)
 }
 
+sub
+watchdog_Undef($$)
+{
+  my ($hash, $name) = @_;
+  RemoveInternalTimer($hash);
+  return undef;
+}
+
 
 1;