diff --git a/lang/src/son/hbvm/regalloc.rs b/lang/src/son/hbvm/regalloc.rs
index c5fcebc..20828d7 100644
--- a/lang/src/son/hbvm/regalloc.rs
+++ b/lang/src/son/hbvm/regalloc.rs
@@ -301,10 +301,10 @@ impl HbvmBackend {
         let bundle_count = self.ralloc.bundles.len() + (reg_offset as usize);
         (
             if tail {
-                bundle_count.saturating_sub(reg::RET_ADDR as _)
-            } else {
                 assert!(bundle_count < reg::STACK_PTR as usize, "TODO: spill memory");
                 self.ralloc.bundles.len()
+            } else {
+                bundle_count.saturating_sub(reg::RET_ADDR as _)
             },
             tail,
         )