diff --git a/rust/nix-expr/src/eval_state.rs b/rust/nix-expr/src/eval_state.rs
index a45c75f..833a366 100644
--- a/rust/nix-expr/src/eval_state.rs
+++ b/rust/nix-expr/src/eval_state.rs
@@ -223,9 +223,9 @@ impl EvalState {
             .with_context(|| "require_attrs_select_opt: attrName contains null byte")?;
         let v2 = unsafe {
             check_call_opt_key!(raw::get_attr_byname[
-                self.context,
+                &mut self.context,
                 v.raw_ptr(),
-                self.raw_ptr(),
+                self.eval_state.as_ptr(),
                 attr_name.as_ptr()
             ])
         }?;
diff --git a/rust/nix-util/src/context.rs b/rust/nix-util/src/context.rs
index cec4063..e838cc6 100644
--- a/rust/nix-util/src/context.rs
+++ b/rust/nix-util/src/context.rs
@@ -107,15 +107,16 @@ pub use check_call;
 macro_rules! check_call_opt_key {
     ($f:path[$ctx:expr, $($arg:expr),*]) => {
         {
-            let ret = $f($ctx.ptr(), $($arg,)*);
-            if unsafe { raw::err_code($ctx.ptr()) == raw::NIX_ERR_KEY } {
-                $ctx.clear();
+            let ctx : &mut $crate::context::Context = $ctx;
+            let ret = $f(ctx.ptr(), $($arg,)*);
+            if unsafe { raw::err_code(ctx.ptr()) == raw::NIX_ERR_KEY } {
+                ctx.clear();
                 return Ok(None);
             }
-            match $ctx.check_err() {
+            match ctx.check_err() {
                 Ok(_) => Ok(Some(ret)),
                 Err(e) => {
-                    $ctx.clear();
+                    ctx.clear();
                     Err(e)
                 }
             }