diff --git a/docs/contributors.rst b/docs/contributors.rst
index 08a828bf19..c2d0b0a698 100644
--- a/docs/contributors.rst
+++ b/docs/contributors.rst
@@ -32,3 +32,4 @@ Contributors include:
 - Nathan Simpson
 - Beojan Stanislaus
 - Daniel Werner
+- Jonas Rembser
diff --git a/src/pyhf/events.py b/src/pyhf/events.py
index f28d0a7563..ae55e2d4f1 100644
--- a/src/pyhf/events.py
+++ b/src/pyhf/events.py
@@ -64,12 +64,20 @@ def _flush(self):
         self._callbacks = _callbacks
 
     def __call__(self, *args, **kwargs):
-        for func, arg in self.callbacks:
+        for func, arg in self._callbacks:
             # weakref: needs to be de-ref'd first before calling
             if arg is not None:
-                func()(arg(), *args, **kwargs)
+                arg_ref = arg()
+                if arg_ref is not None:
+                    func()(arg_ref, *args, **kwargs)
             else:
                 func()(*args, **kwargs)
+        # Flush after calling all the callbacks, not before, as callbacks in the
+        # beginning of the iteration might cause new dead arg weakrefs in
+        # callbacks that are iterated over later.
+        # Checking for dead weakrefs in each iteration and flushing at the end
+        # avoids redundant dead weakref checking in subsequent calls.
+        self._flush()
 
     def __iter__(self):
         return iter(self.callbacks)