diff --git a/crates/fayalite/src/sim.rs b/crates/fayalite/src/sim.rs
index 5d37baf..ab5b7b7 100644
--- a/crates/fayalite/src/sim.rs
+++ b/crates/fayalite/src/sim.rs
@@ -458,6 +458,9 @@ impl Assignments {
             slot_readers
                 .keys_for_assignment(assignment_index)
                 .extend([&assignment.inputs]);
+            slot_readers
+                .keys_for_assignment(assignment_index)
+                .extend(&assignment.conditions);
             let SlotSet(TypeParts {
                 small_slots,
                 big_slots,
@@ -1400,6 +1403,30 @@ impl<'a> Extend<&'a SlotSet> for SlotToAssignmentIndexFullMapKeysForAssignment<'
     }
 }
 
+impl<'a> Extend<&'a Cond> for SlotToAssignmentIndexFullMapKeysForAssignment<'_> {
+    fn extend<T: IntoIterator<Item = &'a Cond>>(&mut self, iter: T) {
+        iter.into_iter().for_each(|cond| match cond.body {
+            CondBody::IfTrue { cond } | CondBody::IfFalse { cond } => {
+                let CompiledValue {
+                    range:
+                        TypeIndexRange {
+                            small_slots,
+                            big_slots,
+                        },
+                    layout: _,
+                    write: _,
+                } = cond;
+                self.extend(small_slots.iter());
+                self.extend(big_slots.iter());
+            }
+            CondBody::MatchArm {
+                discriminant,
+                variant_index: _,
+            } => self.extend([discriminant]),
+        });
+    }
+}
+
 impl Assignment {
     fn new(
         conditions: Interned<[Cond]>,