diff --git a/luisa_compute/src/rtx.rs b/luisa_compute/src/rtx.rs
index 81a115f..a939495 100644
--- a/luisa_compute/src/rtx.rs
+++ b/luisa_compute/src/rtx.rs
@@ -570,7 +570,7 @@ impl SurfaceHitExpr {
         self.inst.ne(u32::MAX)
     }
     pub fn miss(&self) -> Expr<bool> {
-        self.prim.eq(u32::MAX)
+        self.inst.eq(u32::MAX)
     }
     pub fn is_curve(&self) -> Expr<bool> {
         self.bary.y.lt(0.0)
diff --git a/luisa_compute/src/runtime.rs b/luisa_compute/src/runtime.rs
index d9e475e..3df8efe 100644
--- a/luisa_compute/src/runtime.rs
+++ b/luisa_compute/src/runtime.rs
@@ -987,7 +987,15 @@ impl<'a> Scope<'a> {
         callback: F,
     ) {
         self.synchronized.set(false);
-        let api_commands = commands.iter().map(|c| c.inner).collect::<Vec<_>>();
+        let api_commands = commands
+            .iter()
+            .map(|c| c.inner)
+            .filter(|c| match c {
+                // filters zero-size dispatches
+                api::Command::ShaderDispatch(c) => c.dispatch_size.iter().all(|&s| s > 0),
+                _ => true,
+            })
+            .collect::<Vec<_>>();
         let ctx = CommandCallbackCtx {
             commands,
             f: callback,