diff --git a/nih_plug_egui/src/lib.rs b/nih_plug_egui/src/lib.rs
index 19a68cd8..b353e040 100644
--- a/nih_plug_egui/src/lib.rs
+++ b/nih_plug_egui/src/lib.rs
@@ -88,7 +88,7 @@ where
         &self,
         parent: ParentWindowHandle,
         context: Arc<dyn nih_plug::GuiContext>,
-    ) -> Box<dyn std::any::Any> {
+    ) -> Box<dyn std::any::Any + Send + Sync> {
         let update = self.update.clone();
         let state = self.user_state.clone();
 
diff --git a/src/plugin.rs b/src/plugin.rs
index 74b4a182..3e79966b 100644
--- a/src/plugin.rs
+++ b/src/plugin.rs
@@ -204,7 +204,11 @@ pub trait Editor: Send + Sync {
     //       otherwise be basically impossible to have this still be GUI-framework agnostic. Any
     //       callback that deos involve actual GUI operations will still be spooled to the IRunLoop
     //       instance.
-    fn spawn(&self, parent: ParentWindowHandle, context: Arc<dyn GuiContext>) -> Box<dyn Any>;
+    fn spawn(
+        &self,
+        parent: ParentWindowHandle,
+        context: Arc<dyn GuiContext>,
+    ) -> Box<dyn Any + Send + Sync>;
 
     /// Return the (currnent) size of the editor in pixels as a `(width, height)` pair.
     fn size(&self) -> (u32, u32);