diff --git a/crates/backend/src/codegen.rs b/crates/backend/src/codegen.rs
index 45711ba3..8bdd391c 100644
--- a/crates/backend/src/codegen.rs
+++ b/crates/backend/src/codegen.rs
@@ -618,9 +618,6 @@ impl ToTokens for ast::ImportType {
                     fn as_ref(&self) -> &JsValue { &self.obj }
                 }
 
-                impl AsMut<JsValue> for #rust_name {
-                    fn as_mut(&mut self) -> &mut JsValue { &mut self.obj }
-                }
 
                 impl From<#rust_name> for JsValue {
                     fn from(obj: #rust_name) -> JsValue {
@@ -656,12 +653,6 @@ impl ToTokens for ast::ImportType {
                         // wrapper around `val`
                         unsafe { &*(val as *const JsValue as *const #rust_name) }
                     }
-
-                    fn unchecked_from_js_mut(val: &mut JsValue) -> &mut Self {
-                        // Should be safe because `#rust_name` is a transparent
-                        // wrapper around `val`
-                        unsafe { &mut *(val as *mut JsValue as *mut #rust_name) }
-                    }
                 }
 
                 ()
@@ -683,13 +674,6 @@ impl ToTokens for ast::ImportType {
                         #superclass::unchecked_from_js_ref(self.as_ref())
                     }
                 }
-
-                impl AsMut<#superclass> for #rust_name {
-                    fn as_mut(&mut self) -> &mut #superclass {
-                        use wasm_bindgen::JsCast;
-                        #superclass::unchecked_from_js_mut(self.as_mut())
-                    }
-                }
             }).to_tokens(tokens);
         }
     }
@@ -1191,9 +1175,6 @@ impl ToTokens for ast::Dictionary {
                 impl AsRef<JsValue> for #name {
                     fn as_ref(&self) -> &JsValue { self.obj.as_ref() }
                 }
-                impl AsMut<JsValue> for #name {
-                    fn as_mut(&mut self) -> &mut JsValue { self.obj.as_mut() }
-                }
 
                 // Boundary conversion impls
                 impl WasmDescribe for #name {
@@ -1257,10 +1238,6 @@ impl ToTokens for ast::Dictionary {
                     fn unchecked_from_js_ref(val: &JsValue) -> &Self {
                         unsafe { &*(val as *const JsValue as *const #name) }
                     }
-
-                    fn unchecked_from_js_mut(val: &mut JsValue) -> &mut Self {
-                        unsafe { &mut *(val as *mut JsValue as *mut #name) }
-                    }
                 }
             };
         }).to_tokens(tokens);
diff --git a/src/cast.rs b/src/cast.rs
index 928283d3..f856761b 100644
--- a/src/cast.rs
+++ b/src/cast.rs
@@ -14,7 +14,7 @@ use JsValue;
 /// [rfc]: https://github.com/rustwasm/rfcs/pull/2
 pub trait JsCast
 where
-    Self: AsRef<JsValue> + AsMut<JsValue> + Into<JsValue>,
+    Self: AsRef<JsValue> + Into<JsValue>,
 {
     /// Test whether this JS value is an instance of the type `T`.
     ///
@@ -61,24 +61,6 @@ where
         }
     }
 
-    /// Performs a dynamic cast (checked at runtime) of this value into the
-    /// target type `T`.
-    ///
-    /// This method will return `None` is `self.is_instance_of::<T>()`
-    /// returns `false`, and otherwise it will return `Some(&mut T)`
-    /// manufactured with an unchecked cast (verified correct via the
-    /// `instanceof` operation).
-    fn dyn_mut<T>(&mut self) -> Option<&mut T>
-    where
-        T: JsCast,
-    {
-        if self.is_instance_of::<T>() {
-            Some(self.unchecked_mut())
-        } else {
-            None
-        }
-    }
-
     /// Performs a zero-cost unchecked cast into the specified type.
     ///
     /// This method will convert the `self` value to the type `T`, where both
@@ -111,24 +93,6 @@ where
         T::unchecked_from_js_ref(self.as_ref())
     }
 
-    /// Performs a zero-cost unchecked cast into a mutable reference to the
-    /// specified type.
-    ///
-    /// This method will convert the `self` value to the type `T`, where both
-    /// `self` and `T` are simple wrappers around `JsValue`. This method **does
-    /// not check whether `self` is an instance of `T`**. If used incorrectly
-    /// then this method may cause runtime exceptions in both Rust and JS, this
-    /// should be used with caution.
-    ///
-    /// This method, unlike `unchecked_into`, does not consume ownership of
-    /// `self` and instead works over a utable reference.
-    fn unchecked_mut<T>(&mut self) -> &mut T
-    where
-        T: JsCast,
-    {
-        T::unchecked_from_js_mut(self.as_mut())
-    }
-
     /// Performs a dynamic `instanceof` check to see whether the `JsValue`
     /// provided is an instance of this type.
     ///
@@ -152,14 +116,4 @@ where
     /// This is intended to be an internal implementation detail, you likely
     /// won't need to call this.
     fn unchecked_from_js_ref(val: &JsValue) -> &Self;
-
-    /// Performs a zero-cost unchecked conversion from a `&mut JsValue` into an
-    /// instance of `&mut Self`.
-    ///
-    /// Note the safety of this method, which basically means that `Self` must
-    /// be a newtype wrapper around `JsValue`.
-    ///
-    /// This is intended to be an internal implementation detail, you likely
-    /// won't need to call this.
-    fn unchecked_from_js_mut(val: &mut JsValue) -> &mut Self;
 }
diff --git a/src/lib.rs b/src/lib.rs
index 7c9ce9f9..b26c872d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -370,11 +370,6 @@ impl JsCast for JsValue {
     fn instanceof(_val: &JsValue) -> bool { true }
     fn unchecked_from_js(val: JsValue) -> Self { val }
     fn unchecked_from_js_ref(val: &JsValue) -> &Self { val }
-    fn unchecked_from_js_mut(val: &mut JsValue) -> &mut Self { val }
-}
-
-impl AsMut<JsValue> for JsValue {
-    fn as_mut(&mut self) -> &mut JsValue { self }
 }
 
 impl AsRef<JsValue> for JsValue {