diff --git a/src/js/clops2js.mbt b/src/js/clops2js.mbt
index 28e11d9..7ddeaf2 100644
--- a/src/js/clops2js.mbt
+++ b/src/js/clops2js.mbt
@@ -182,12 +182,11 @@ pub fn JsEmitter::emit(self : JsEmitter) -> String {
   output += line_start
   // B. emit all functions
   output += line_start + "const compiled_functions = ["
-
+  let line_start = "\n  "
   // 1. emit root
   output += line_start + "function() { // root"
   output += self.indent().indent().emit_cps(self.clops.root)
   output += line_start + "},"
-
   // 2. emit all functions
   for label in self.lid2label {
     let cur_fn = self.clops.fnblocks[label].unwrap()
@@ -197,7 +196,7 @@ pub fn JsEmitter::emit(self : JsEmitter) -> String {
     let args_with_closure_emitted = args_with_closure.map(emit_var).join(", ")
     output += line_start +
       "function(\{args_with_closure_emitted}) { // \{label}"
-    // i. emit body
+    // ii. emit body
     output += self.indent().indent().emit_cps(cur_fn.body)
     output += line_start + "},"
   }
diff --git a/src/riscv/codegen.mbt b/src/riscv/codegen.mbt
index afa02c7..fac9166 100644
--- a/src/riscv/codegen.mbt
+++ b/src/riscv/codegen.mbt
@@ -89,7 +89,11 @@ fn CodegenBlock::new(
   let params = cfg.fn_args[name_var].unwrap()
   for param in params {
     let alloc_reg = allocation[param].unwrap()
-    dirtied.insert(alloc_reg)
+    if cfg.spilled.contains(param) {
+      @util.die("param \{param} of fn \{name_var} spilled")
+    } else {
+      dirtied.insert(alloc_reg)
+    }
   }
 
   // 3. collect spilled vars
diff --git a/src/riscv/reg_allocation.mbt b/src/riscv/reg_allocation.mbt
index 76f4d88..5546b38 100644
--- a/src/riscv/reg_allocation.mbt
+++ b/src/riscv/reg_allocation.mbt
@@ -66,14 +66,22 @@ fn reg_allocate_on_fn(
       vars_f, graph_f, alloc_fregs, allocation_f, simplify_stack_f,
     )
     if should_spill_i {
+      let vars_i_spillable = vars_i
+        .iter()
+        .filter(fn(var) { not(allocation_i.contains(var)) })
+        |> @hashset.from_iter()
       let i_spilled = reg_spill_fn(
-        input, vars_i, simplify_stack_i, graph_i, fn_label,
+        input, vars_i_spillable, simplify_stack_i, graph_i, fn_label,
       )
       spilled_set.insert(i_spilled)
     }
     if should_spill_f {
+      let vars_f_spillable = vars_i
+        .iter()
+        .filter(fn(var) { not(allocation_f.contains(var)) })
+        |> @hashset.from_iter()
       let f_spilled = reg_spill_fn(
-        input, vars_f, simplify_stack_f, graph_f, fn_label,
+        input, vars_f_spillable, simplify_stack_f, graph_f, fn_label,
       )
       spilled_set.insert(f_spilled)
     }
diff --git a/src/riscv/reg_spill.mbt b/src/riscv/reg_spill.mbt
index 3c477c9..0ddc14e 100644
--- a/src/riscv/reg_spill.mbt
+++ b/src/riscv/reg_spill.mbt
@@ -1,11 +1,11 @@
 fn reg_spill_fn(
   cfg : @ssacfg.SsaCfg,
-  all_vars : @hashset.T[Var],
-  can_allocate : Array[Var],
+  all_vars_not_preallocated : @hashset.T[Var],
+  can_allocate : Array[Var], // vars that can be allocated but not yet
   interference : InterferenceGraph,
   fn_name : Var
 ) -> Var {
-  let spill_candidates = all_vars
+  let spill_candidates = all_vars_not_preallocated
     .iter()
     .filter(fn(var) { not(can_allocate.contains(var)) })
     .collect()