diff --git a/core/src/avm2/activation.rs b/core/src/avm2/activation.rs
index 452247aa2..c5360e8bd 100644
--- a/core/src/avm2/activation.rs
+++ b/core/src/avm2/activation.rs
@@ -1384,7 +1384,7 @@ impl<'a, 'gc, 'gc_context> Activation<'a, 'gc, 'gc_context> {
 
     fn op_get_slot(&mut self, index: u32) -> Result<FrameControl<'gc>, Error> {
         let object = self.context.avm2.pop().coerce_to_object(self)?;
-        let value = object.get_slot(index)?;
+        let value = object.get_slot(self, index)?;
 
         self.context.avm2.push(value);
 
@@ -1395,13 +1395,13 @@ impl<'a, 'gc, 'gc_context> Activation<'a, 'gc, 'gc_context> {
         let value = self.context.avm2.pop();
         let object = self.context.avm2.pop().coerce_to_object(self)?;
 
-        object.set_slot(index, value, self.context.gc_context)?;
+        object.set_slot(self, index, value)?;
 
         Ok(FrameControl::Continue)
     }
 
     fn op_get_global_slot(&mut self, index: u32) -> Result<FrameControl<'gc>, Error> {
-        let value = self.scope.unwrap().read().globals().get_slot(index)?;
+        let value = self.scope.unwrap().read().globals().get_slot(self, index)?;
 
         self.context.avm2.push(value);
 
@@ -1415,7 +1415,7 @@ impl<'a, 'gc, 'gc_context> Activation<'a, 'gc, 'gc_context> {
             .unwrap()
             .read()
             .globals()
-            .set_slot(index, value, self.context.gc_context)?;
+            .set_slot(self, index, value)?;
 
         Ok(FrameControl::Continue)
     }
diff --git a/core/src/avm2/object.rs b/core/src/avm2/object.rs
index 2415f0394..7c9856033 100644
--- a/core/src/avm2/object.rs
+++ b/core/src/avm2/object.rs
@@ -207,11 +207,49 @@ pub trait TObject<'gc>: 'gc + Collect + Debug + Into<Object<'gc>> + Clone + Copy
         receiver.init_property_local(receiver, name, value, activation)
     }
 
+    /// Determines if a local slot already exists and is occupied.
+    fn has_slot_local(self, id: u32) -> bool;
+
     /// Retrieve a slot by its index.
-    fn get_slot(self, id: u32) -> Result<Value<'gc>, Error>;
+    #[allow(unused_mut)]
+    fn get_slot(
+        mut self,
+        activation: &mut Activation<'_, 'gc, '_>,
+        id: u32,
+    ) -> Result<Value<'gc>, Error> {
+        if !self.has_slot_local(id) {
+            let slot_trait = self
+                .get_trait_slot(id)?
+                .ok_or_else(|| format!("Slot index {} out of bounds!", id))?;
+            self.install_trait(activation, slot_trait, self.into())?;
+        }
+
+        self.get_slot_local(id)
+    }
+
+    /// Retrieve a slot by its index, ignoring uninstalled traits.
+    fn get_slot_local(self, id: u32) -> Result<Value<'gc>, Error>;
 
     /// Set a slot by its index.
+    #[allow(unused_mut)]
     fn set_slot(
+        mut self,
+        activation: &mut Activation<'_, 'gc, '_>,
+        id: u32,
+        value: Value<'gc>,
+    ) -> Result<(), Error> {
+        if !self.has_slot_local(id) {
+            let slot_trait = self
+                .get_trait_slot(id)?
+                .ok_or_else(|| format!("Slot index {} out of bounds!", id))?;
+            self.install_trait(activation, slot_trait, self.into())?;
+        }
+
+        self.set_slot_local(id, value, activation.context.gc_context)
+    }
+
+    /// Set a slot by its index, ignoring uninstalled traits.
+    fn set_slot_local(
         self,
         id: u32,
         value: Value<'gc>,
@@ -219,7 +257,25 @@ pub trait TObject<'gc>: 'gc + Collect + Debug + Into<Object<'gc>> + Clone + Copy
     ) -> Result<(), Error>;
 
     /// Initialize a slot by its index.
+    #[allow(unused_mut)]
     fn init_slot(
+        mut self,
+        activation: &mut Activation<'_, 'gc, '_>,
+        id: u32,
+        value: Value<'gc>,
+    ) -> Result<(), Error> {
+        if !self.has_slot_local(id) {
+            let slot_trait = self
+                .get_trait_slot(id)?
+                .ok_or_else(|| format!("Slot index {} out of bounds!", id))?;
+            self.install_trait(activation, slot_trait, self.into())?;
+        }
+
+        self.init_slot_local(id, value, activation.context.gc_context)
+    }
+
+    /// Initialize a slot by its index, ignoring uninstalled traits.
+    fn init_slot_local(
         self,
         id: u32,
         value: Value<'gc>,
diff --git a/core/src/avm2/object/custom_object.rs b/core/src/avm2/object/custom_object.rs
index 4147f5461..07e2aedd6 100644
--- a/core/src/avm2/object/custom_object.rs
+++ b/core/src/avm2/object/custom_object.rs
@@ -94,26 +94,30 @@ macro_rules! impl_avm2_custom_object_properties {
 #[macro_export]
 macro_rules! impl_avm2_custom_object {
     ($field:ident) => {
-        fn get_slot(self, id: u32) -> Result<Value<'gc>, Error> {
-            self.0.read().$field.get_slot(id)
+        fn has_slot_local(self, id: u32) -> bool {
+            self.0.read().$field.has_slot_local(id)
         }
 
-        fn set_slot(
+        fn get_slot_local(self, id: u32) -> Result<Value<'gc>, Error> {
+            self.0.read().$field.get_slot_local(id)
+        }
+
+        fn set_slot_local(
             self,
             id: u32,
             value: Value<'gc>,
             mc: MutationContext<'gc, '_>,
         ) -> Result<(), Error> {
-            self.0.write(mc).$field.set_slot(id, value, mc)
+            self.0.write(mc).$field.set_slot_local(id, value, mc)
         }
 
-        fn init_slot(
+        fn init_slot_local(
             self,
             id: u32,
             value: Value<'gc>,
             mc: MutationContext<'gc, '_>,
         ) -> Result<(), Error> {
-            self.0.write(mc).$field.init_slot(id, value, mc)
+            self.0.write(mc).$field.init_slot_local(id, value, mc)
         }
 
         fn get_method(self, id: u32) -> Option<Object<'gc>> {
diff --git a/core/src/avm2/object/script_object.rs b/core/src/avm2/object/script_object.rs
index 64f2a88b8..279de26d7 100644
--- a/core/src/avm2/object/script_object.rs
+++ b/core/src/avm2/object/script_object.rs
@@ -134,26 +134,30 @@ impl<'gc> TObject<'gc> for ScriptObject<'gc> {
         self.0.write(gc_context).delete_property(name)
     }
 
-    fn get_slot(self, id: u32) -> Result<Value<'gc>, Error> {
-        self.0.read().get_slot(id)
+    fn has_slot_local(self, id: u32) -> bool {
+        self.0.read().has_slot_local(id)
     }
 
-    fn set_slot(
+    fn get_slot_local(self, id: u32) -> Result<Value<'gc>, Error> {
+        self.0.read().get_slot_local(id)
+    }
+
+    fn set_slot_local(
         self,
         id: u32,
         value: Value<'gc>,
         mc: MutationContext<'gc, '_>,
     ) -> Result<(), Error> {
-        self.0.write(mc).set_slot(id, value, mc)
+        self.0.write(mc).set_slot_local(id, value, mc)
     }
 
-    fn init_slot(
+    fn init_slot_local(
         self,
         id: u32,
         value: Value<'gc>,
         mc: MutationContext<'gc, '_>,
     ) -> Result<(), Error> {
-        self.0.write(mc).init_slot(id, value, mc)
+        self.0.write(mc).init_slot_local(id, value, mc)
     }
 
     fn get_method(self, id: u32) -> Option<Object<'gc>> {
@@ -467,7 +471,9 @@ impl<'gc> ScriptObjectData<'gc> {
         };
 
         if let Some(slot_id) = slot_id {
-            self.set_slot(slot_id, value, activation.context.gc_context)?;
+            // This doesn't need the non-local version of this property because
+            // by the time this has called the slot was already installed
+            self.set_slot_local(slot_id, value, activation.context.gc_context)?;
             Ok(Value::Undefined.into())
         } else if self.values.contains_key(name) {
             let prop = self.values.get_mut(name).unwrap();
@@ -492,7 +498,10 @@ impl<'gc> ScriptObjectData<'gc> {
     ) -> Result<ReturnValue<'gc>, Error> {
         if let Some(prop) = self.values.get_mut(name) {
             if let Some(slot_id) = prop.slot_id() {
-                self.init_slot(slot_id, value, activation.context.gc_context)?;
+                // This doesn't need the non-local version of this property
+                // because by the time this has called the slot was already
+                // installed
+                self.init_slot_local(slot_id, value, activation.context.gc_context)?;
                 Ok(Value::Undefined.into())
             } else {
                 let proto = self.proto;
@@ -528,8 +537,14 @@ impl<'gc> ScriptObjectData<'gc> {
         can_delete
     }
 
-    pub fn get_slot(&self, id: u32) -> Result<Value<'gc>, Error> {
-        //TODO: slot inheritance, I think?
+    pub fn has_slot_local(&self, id: u32) -> bool {
+        self.slots
+            .get(id as usize)
+            .map(|s| s.is_occupied())
+            .unwrap_or(false)
+    }
+
+    pub fn get_slot_local(&self, id: u32) -> Result<Value<'gc>, Error> {
         self.slots
             .get(id as usize)
             .cloned()
@@ -538,7 +553,7 @@ impl<'gc> ScriptObjectData<'gc> {
     }
 
     /// Set a slot by its index.
-    pub fn set_slot(
+    pub fn set_slot_local(
         &mut self,
         id: u32,
         value: Value<'gc>,
@@ -551,8 +566,8 @@ impl<'gc> ScriptObjectData<'gc> {
         }
     }
 
-    /// Set a slot by its index.
-    pub fn init_slot(
+    /// Initialize a slot by its index.
+    pub fn init_slot_local(
         &mut self,
         id: u32,
         value: Value<'gc>,
diff --git a/core/src/avm2/object/stage_object.rs b/core/src/avm2/object/stage_object.rs
index a04be5dd2..520331708 100644
--- a/core/src/avm2/object/stage_object.rs
+++ b/core/src/avm2/object/stage_object.rs
@@ -135,26 +135,30 @@ impl<'gc> TObject<'gc> for StageObject<'gc> {
         self.0.write(gc_context).base.delete_property(multiname)
     }
 
-    fn get_slot(self, id: u32) -> Result<Value<'gc>, Error> {
-        self.0.read().base.get_slot(id)
+    fn has_slot_local(self, id: u32) -> bool {
+        self.0.read().base.has_slot_local(id)
     }
 
-    fn set_slot(
+    fn get_slot_local(self, id: u32) -> Result<Value<'gc>, Error> {
+        self.0.read().base.get_slot_local(id)
+    }
+
+    fn set_slot_local(
         self,
         id: u32,
         value: Value<'gc>,
         mc: MutationContext<'gc, '_>,
     ) -> Result<(), Error> {
-        self.0.write(mc).base.set_slot(id, value, mc)
+        self.0.write(mc).base.set_slot_local(id, value, mc)
     }
 
-    fn init_slot(
+    fn init_slot_local(
         self,
         id: u32,
         value: Value<'gc>,
         mc: MutationContext<'gc, '_>,
     ) -> Result<(), Error> {
-        self.0.write(mc).base.init_slot(id, value, mc)
+        self.0.write(mc).base.init_slot_local(id, value, mc)
     }
 
     fn get_method(self, id: u32) -> Option<Object<'gc>> {
diff --git a/core/src/avm2/property.rs b/core/src/avm2/property.rs
index de6b061be..3321aab54 100644
--- a/core/src/avm2/property.rs
+++ b/core/src/avm2/property.rs
@@ -142,7 +142,10 @@ impl<'gc> Property<'gc> {
             )),
             Property::Virtual { get: None, .. } => Ok(Value::Undefined.into()),
             Property::Stored { value, .. } => Ok(value.to_owned().into()),
-            Property::Slot { slot_id, .. } => this.get_slot(*slot_id).map(|v| v.into()),
+
+            // This doesn't need the non-local version of this property because
+            // by the time this has called the slot was already installed
+            Property::Slot { slot_id, .. } => this.get_slot_local(*slot_id).map(|v| v.into()),
         }
     }
 
diff --git a/core/src/avm2/slot.rs b/core/src/avm2/slot.rs
index 3007bdaea..844fdecb1 100644
--- a/core/src/avm2/slot.rs
+++ b/core/src/avm2/slot.rs
@@ -86,4 +86,8 @@ impl<'gc> Slot<'gc> {
             }
         }
     }
+
+    pub fn is_occupied(&self) -> bool {
+        matches!(self, Slot::Occupied { .. })
+    }
 }