diff --git a/nix-js/runtime-ts/src/index.ts b/nix-js/runtime-ts/src/index.ts
index 867a1c7..e515e54 100644
--- a/nix-js/runtime-ts/src/index.ts
+++ b/nix-js/runtime-ts/src/index.ts
@@ -23,7 +23,7 @@ import { op } from "./operators";
 import { builtins, PRIMOP_METADATA } from "./builtins";
 import { coerceToString, StringCoercionMode } from "./builtins/conversion";
 import { HAS_CONTEXT } from "./string-context";
-import { IS_PATH, mkFunction } from "./types";
+import { IS_PATH, mkAttrs, mkFunction } from "./types";
 import { forceBool } from "./type-assert";
 
 export type NixRuntime = typeof Nix;
@@ -52,6 +52,7 @@ export const Nix = {
   coerceToString,
   concatStringsWithContext,
   StringCoercionMode,
+  mkAttrs,
   mkFunction,
 
   pushContext,
diff --git a/nix-js/runtime-ts/src/types.ts b/nix-js/runtime-ts/src/types.ts
index 6537288..ab4982a 100644
--- a/nix-js/runtime-ts/src/types.ts
+++ b/nix-js/runtime-ts/src/types.ts
@@ -2,10 +2,11 @@
  * Core TypeScript type definitions for nix-js runtime
  */
 
-import { IS_THUNK } from "./thunk";
-import { type StringWithContext, HAS_CONTEXT, isStringWithContext } from "./string-context";
+import { force, IS_THUNK } from "./thunk";
+import { type StringWithContext, HAS_CONTEXT, isStringWithContext, getStringContext } from "./string-context";
 import { op } from "./operators";
 import { forceAttrs } from "./type-assert";
+import { isString, typeOf } from "./builtins/type-check";
 export { HAS_CONTEXT, isStringWithContext };
 export type { StringWithContext };
 
@@ -73,6 +74,24 @@ export const mkFunction = (
   return func;
 };
 
+export const mkAttrs = (attrs: NixAttrs, keys: NixValue[], values: NixValue[]): NixAttrs => {
+  const len = keys.length;
+  for (let i = 0; i < len; i++) {
+    const key = force(keys[i]);
+    if (key === null) {
+      continue;
+    }
+    if (!isString(key)) {
+      throw `Expected string, got ${typeOf(key)}`
+    }
+    if (isStringWithContext(key)) {
+      throw new TypeError(`the string '${key.value}' is not allowed to refer to a store path`)
+    }
+    attrs[key] = values[i];
+  }
+  return attrs;
+};
+
 /**
  * Interface for lazy thunk values
  * Thunks delay evaluation until forced
diff --git a/nix-js/src/codegen.rs b/nix-js/src/codegen.rs
index cec2772..b0bb598 100644
--- a/nix-js/src/codegen.rs
+++ b/nix-js/src/codegen.rs
@@ -353,24 +353,28 @@ impl<Ctx: CodegenContext> Compile<Ctx> for AttrSet {
             attrs.push(format!("{}:{}", key.escape_quote(), value));
         }
 
-        // FIXME: duplicated key
-        for (key_expr, value_expr) in &self.dyns {
-            let key = ctx.get_ir(*key_expr).compile(ctx);
-            let value_code = ctx.get_ir(*value_expr).compile(ctx);
-
-            let value = if stack_trace_enabled {
-                let value_span = encode_span(ctx.get_ir(*value_expr).span(), ctx);
-                format!(
-                    "Nix.withContext(\"while evaluating a dynamic attribute\",{},()=>({}))",
-                    value_span, value_code
-                )
-            } else {
-                value_code
-            };
-            attrs.push(format!("[{}]:{}", key, value));
+        if !self.dyns.is_empty() {
+            let (keys, vals) = self.dyns.iter().map(|&(key, val)| {
+                let key = ctx.get_ir(key).compile(ctx);
+                let val_expr = ctx.get_ir(val);
+                let val = val_expr.compile(ctx);
+                let span = val_expr.span();
+                let val = if stack_trace_enabled {
+                    let span = encode_span(span, ctx);
+                    format!(
+                        "Nix.withContext(\"while evaluating a dynamic attribute\",{},()=>({}))",
+                        span, val
+                    )
+                } else {
+                    val
+                };
+                (key, val)
+            }).collect::<(Vec<_>, Vec<_>)>();
+            format!("Nix.mkAttrs({{{}}},[{}],[{}])", attrs.join(","), keys.join(","), vals.join(","))
+        } else {
+            format!("{{{}}}", attrs.join(","))
         }
 
-        format!("{{{}}}", attrs.join(","))
     }
 }