diff --git a/elfo-core/src/supervisor.rs b/elfo-core/src/supervisor.rs
index e398fe1d..54e7cba3 100644
--- a/elfo-core/src/supervisor.rs
+++ b/elfo-core/src/supervisor.rs
@@ -1,6 +1,4 @@
-use std::{
-    any::Any, future::Future, mem, ops::Deref, panic::AssertUnwindSafe, sync::Arc, time::Duration,
-};
+use std::{any::Any, future::Future, mem, panic::AssertUnwindSafe, sync::Arc, time::Duration};
 
 use dashmap::DashMap;
 use futures::{future::BoxFuture, FutureExt};
@@ -226,14 +224,24 @@ where
                 None => visitor.empty(envelope),
             },
             Outcome::Multicast(list) => {
-                let iter = list.into_iter().filter_map(|key| get_or_spawn!(self, key));
-                self.visit_multiple(envelope, visitor, iter);
+                let keys = list
+                    .into_iter()
+                    .filter(|key| get_or_spawn!(self, key.clone()).is_some())
+                    .collect();
+                self.visit_multiple(envelope, visitor, keys);
             }
             Outcome::GentleMulticast(list) => {
-                let iter = list.into_iter().filter_map(|key| self.objects.get(&key));
-                self.visit_multiple(envelope, visitor, iter);
+                let keys = list
+                    .into_iter()
+                    .filter(|key| self.objects.get(key).is_some())
+                    .collect();
+                self.visit_multiple(envelope, visitor, keys);
             }
-            Outcome::Broadcast => self.visit_multiple(envelope, visitor, self.objects.iter()),
+            Outcome::Broadcast => self.visit_multiple(
+                envelope,
+                visitor,
+                self.objects.iter().map(|o| o.key().clone()).collect(),
+            ),
             Outcome::Discard => visitor.empty(envelope),
             Outcome::Default => unreachable!("must be altered earlier"),
         }
@@ -243,22 +251,22 @@ where
         &self,
         envelope: Envelope,
         visitor: &mut dyn GroupVisitor,
-        iter: impl Iterator<Item = impl Deref<Target = ObjectArc>>,
+        // TODO: get rid of this allocation
+        keys: Vec<R::Key>,
     ) {
-        let mut iter = iter.peekable();
-
-        if iter.peek().is_none() {
-            return visitor.empty(envelope);
-        }
-
-        loop {
-            let object = iter.next().unwrap();
-            if iter.peek().is_none() {
-                return visitor.visit_last(&object, envelope);
+        let len = keys.len();
+        for (index, key) in keys.into_iter().enumerate() {
+            let item = self.objects.get(&key).unwrap();
+            if index + 1 == len {
+                visitor.visit_last(&item, envelope);
+                return;
             } else {
-                visitor.visit(&object, &envelope);
+                visitor.visit(&item, &envelope);
             }
         }
+        if len == 0 {
+            visitor.empty(envelope);
+        }
     }
 
     fn spawn(self: &Arc<Self>, key: R::Key, mut backoff: Backoff) -> Option<ObjectArc> {