diff --git a/src/callback.rs b/src/callback.rs
index f6a9a3c..ca93abe 100644
--- a/src/callback.rs
+++ b/src/callback.rs
@@ -111,7 +111,7 @@ macro_rules! impl_tuple {
                 let system_fn = move |args: In<Vec<RN::Value>>, world: &mut World| {
                     let mut runtime = world.get_resource_mut::<RN>().expect("No runtime resource");
                     let args  = if RN::needs_own_thread() {
-                        runtime.with_engine_thread_mut(move |engine| {
+                        runtime.with_engine_send_mut(move |engine| {
                             (
                                 $($t::from_runtime_value_with_engine(args.get($idx).expect(&format!("Failed to get function argument for index {}", $idx)).clone(), engine), )+
                             )
@@ -128,7 +128,7 @@ macro_rules! impl_tuple {
                     inner_system.apply_deferred(world);
                     let mut runtime = world.get_resource_mut::<RN>().expect("No runtime resource");
                     if RN::needs_own_thread() {
-                        runtime.with_engine_thread_mut(move |engine| {
+                        runtime.with_engine_send_mut(move |engine| {
                             Out::into_runtime_value_with_engine(result, engine)
                         })
                     } else {
diff --git a/src/runtimes/ruby.rs b/src/runtimes/ruby.rs
index 31a0358..eaba3bf 100644
--- a/src/runtimes/ruby.rs
+++ b/src/runtimes/ruby.rs
@@ -338,11 +338,15 @@ impl Runtime for RubyRuntime {
     }
 
     fn with_engine_mut<T>(&mut self, _f: impl FnOnce(&mut Self::RawEngine) -> T) -> T {
-        unimplemented!("Ruby requires single threaded execution, use `with_engine_thread`");
+        unimplemented!(
+            "Ruby runtime requires sending execution to another thread, use `with_engine_mut_send`"
+        );
     }
 
     fn with_engine<T>(&self, _f: impl FnOnce(&Self::RawEngine) -> T) -> T {
-        unimplemented!("Ruby requires single threaded execution, use `with_engine_thread`");
+        unimplemented!(
+            "Ruby runtime requires sending execution to another thread, use `with_engine_send`"
+        );
     }
 
     fn eval(