diff --git a/crates/cli-support/src/descriptor.rs b/crates/cli-support/src/descriptor.rs
index 0ec60db8e..bd6bc25f7 100644
--- a/crates/cli-support/src/descriptor.rs
+++ b/crates/cli-support/src/descriptor.rs
@@ -48,7 +48,7 @@ pub enum Descriptor {
     F64,
     Boolean,
     Function(Box<Function>),
-    Closure(Box<Function>, bool),
+    Closure(Box<Closure>),
     Ref(Box<Descriptor>),
     RefMut(Box<Descriptor>),
     Slice(Box<Descriptor>),
@@ -65,6 +65,12 @@ pub struct Function {
     pub ret: Option<Descriptor>,
 }
 
+#[derive(Debug)]
+pub struct Closure {
+    pub function: Function,
+    pub mutable: bool,
+}
+
 #[derive(Copy, Clone)]
 pub enum VectorKind {
     I8,
@@ -100,11 +106,7 @@ impl Descriptor {
             F64 => Descriptor::F64,
             BOOLEAN => Descriptor::Boolean,
             FUNCTION => Descriptor::Function(Box::new(Function::decode(data))),
-            CLOSURE => {
-                let mutable = get(data) == REFMUT;
-                assert_eq!(get(data), FUNCTION);
-                Descriptor::Closure(Box::new(Function::decode(data)), mutable)
-            }
+            CLOSURE => Descriptor::Closure(Box::new(Closure::decode(data))),
             REF => Descriptor::Ref(Box::new(Descriptor::_decode(data))),
             REFMUT => Descriptor::RefMut(Box::new(Descriptor::_decode(data))),
             SLICE => Descriptor::Slice(Box::new(Descriptor::_decode(data))),
@@ -153,16 +155,16 @@ impl Descriptor {
         }
     }
 
-    pub fn ref_closure(&self) -> Option<(&Function, bool)> {
+    pub fn ref_closure(&self) -> Option<&Closure> {
         match *self {
             Descriptor::Ref(ref s) => s.closure(),
             _ => None,
         }
     }
 
-    pub fn closure(&self) -> Option<(&Function, bool)> {
+    pub fn closure(&self) -> Option<&Closure> {
         match *self {
-            Descriptor::Closure(ref s, mutable) => Some((s, mutable)),
+            Descriptor::Closure(ref s) => Some(s),
             _ => None,
         }
     }
@@ -240,6 +242,17 @@ fn get(a: &mut &[u32]) -> u32 {
     ret
 }
 
+impl Closure {
+    fn decode(data: &mut &[u32]) -> Closure {
+        let mutable = get(data) == REFMUT;
+        assert_eq!(get(data), FUNCTION);
+        Closure {
+            mutable,
+            function: Function::decode(data),
+        }
+    }
+}
+
 impl Function {
     fn decode(data: &mut &[u32]) -> Function {
         let arguments = (0..get(data))
diff --git a/crates/cli-support/src/js/rust2js.rs b/crates/cli-support/src/js/rust2js.rs
index e9412d7cb..111aca481 100644
--- a/crates/cli-support/src/js/rust2js.rs
+++ b/crates/cli-support/src/js/rust2js.rs
@@ -140,10 +140,10 @@ impl<'a, 'b> Rust2Js<'a, 'b> {
             return
         }
 
-        if let Some((f, mutable)) = arg.ref_closure() {
+        if let Some(closure) = arg.ref_closure() {
             let (js, _ts) = {
                 let mut builder = Js2Rust::new("", self.cx);
-                if mutable {
+                if closure.mutable {
                     builder.prelude("let a = this.a;\n")
                         .prelude("this.a = 0;\n")
                         .rust_argument("a")
@@ -153,7 +153,7 @@ impl<'a, 'b> Rust2Js<'a, 'b> {
                 }
                 builder
                     .rust_argument("this.b")
-                    .process(f)
+                    .process(&closure.function)
                     .finish("function", "this.f")
             };
             self.cx.expose_get_global_argument();