diff --git a/crates/wasm-bindgen-cli-support/src/js.rs b/crates/wasm-bindgen-cli-support/src/js.rs
index 774f47f3..faba08eb 100644
--- a/crates/wasm-bindgen-cli-support/src/js.rs
+++ b/crates/wasm-bindgen-cli-support/src/js.rs
@@ -1031,7 +1031,7 @@ impl<'a, 'b> SubContext<'a, 'b> {
                     ", i = i, func = func, arg = name));
                     pass(&format!("ptr{}", i));
                     pass(&format!("len{}", i));
-                    if ty.owned {
+                    if !ty.owned {
                         destructors.push_str(&format!("\n\
                             wasm.__wbindgen_free(ptr{i}, len{i});\n\
                         ", i = i));
diff --git a/crates/wasm-bindgen-macro/src/lib.rs b/crates/wasm-bindgen-macro/src/lib.rs
index 92bc40ef..1878bb00 100644
--- a/crates/wasm-bindgen-macro/src/lib.rs
+++ b/crates/wasm-bindgen-macro/src/lib.rs
@@ -148,7 +148,7 @@ fn bindgen_export(export: &ast::Export, into: &mut Tokens) {
                 let ptr = syn::Ident::from(format!("arg{}_ptr", i));
                 let len = syn::Ident::from(format!("arg{}_len", i));
                 let abi_ty = ty.abi_element();
-                args.push(my_quote! { #ptr: *const #abi_ty });
+                args.push(my_quote! { #ptr: *mut #abi_ty });
                 args.push(my_quote! { #len: usize });
                 if owned {
                     arg_conversions.push(my_quote! {
@@ -159,7 +159,7 @@ fn bindgen_export(export: &ast::Export, into: &mut Tokens) {
                 } else {
                     arg_conversions.push(my_quote! {
                         let #ident = unsafe {
-                            ::std::slice::from_raw_parts(#ptr, #len)
+                            ::std::slice::from_raw_parts(#ptr as *const #abi_ty, #len)
                         };
                     });
                 }
diff --git a/crates/wasm-bindgen-shared/src/lib.rs b/crates/wasm-bindgen-shared/src/lib.rs
index d497ef18..7fe56b5d 100644
--- a/crates/wasm-bindgen-shared/src/lib.rs
+++ b/crates/wasm-bindgen-shared/src/lib.rs
@@ -100,7 +100,7 @@ pub const TYPE_SLICE_F64: char = '\u{71}';
 pub const TYPE_JS_OWNED: char = '\u{72}';
 pub const TYPE_JS_REF: char = '\u{73}';
 
-pub const TYPE_CUSTOM_START: u32 = 0x64;
+pub const TYPE_CUSTOM_START: u32 = 0x74;
 pub const TYPE_CUSTOM_REF_FLAG: u32 = 1;
 
 pub fn name_to_descriptor(name: &str) -> char {