--- a/crates/jrsonnet-evaluator/src/error.rs
+++ b/crates/jrsonnet-evaluator/src/error.rs
@@ -63,6 +63,8 @@
 
 	#[error("field name should be string, got {0}")]
 	FieldMustBeStringGot(ValType),
+	#[error("duplicate field name: {0}")]
+	DuplicateFieldName(IStr),
 
 	#[error("attempted to index array with string {0}")]
 	AttemptedIndexAnArrayWithString(IStr),
--- a/crates/jrsonnet-evaluator/src/evaluate/mod.rs
+++ b/crates/jrsonnet-evaluator/src/evaluate/mod.rs
@@ -298,7 +298,7 @@
 						context_creator: context_creator.clone(),
 						value: value.clone(),
 						name,
-					})));
+					})))?;
 			}
 			Member::Field(FieldMember {
 				name,
@@ -341,7 +341,7 @@
 						value: value.clone(),
 						params: params.clone(),
 						name,
-					})));
+					})))?;
 			}
 			Member::BindStmt(_) => {}
 			Member::AssertStmt(stmt) => {
@@ -424,7 +424,7 @@
 							.bindable(TraceBox(Box::new(ObjCompBinding {
 								context: ctx,
 								value: obj.value.clone(),
-							})));
+							})))?;
 					}
 					v => throw!(FieldMustBeStringGot(v.value_type())),
 				}
--- a/crates/jrsonnet-evaluator/src/integrations/serde.rs
+++ b/crates/jrsonnet-evaluator/src/integrations/serde.rs
@@ -68,7 +68,7 @@
 			Value::Object(o) => {
 				let mut builder = ObjValueBuilder::with_capacity(o.len());
 				for (k, v) in o {
-					builder.member((k as &str).into()).value(v.try_into()?);
+					builder.member((k as &str).into()).value(v.try_into()?)?;
 				}
 				Self::Obj(builder.build())
 			}
--- a/crates/jrsonnet-evaluator/src/obj.rs
+++ b/crates/jrsonnet-evaluator/src/obj.rs
@@ -1,6 +1,11 @@
+use crate::function::CallLocation;
 use crate::gc::{GcHashMap, GcHashSet, TraceBox};
 use crate::operator::evaluate_add_op;
-use crate::{cc_ptr_eq, weak_ptr_eq, weak_raw, Bindable, LazyBinding, LazyVal, Result, Val};
+use crate::push_frame;
+use crate::{
+	cc_ptr_eq, error::Error::*, throw, weak_ptr_eq, weak_raw, Bindable, LazyBinding, LazyVal,
+	Result, Val,
+};
 use gcmodule::{Cc, Trace, Weak};
 use jrsonnet_interner::IStr;
 use jrsonnet_parser::{ExprLocation, Visibility};
@@ -373,22 +378,29 @@
 		self.location = Some(location);
 		self
 	}
-	pub fn value(self, value: Val) -> &'v mut ObjValueBuilder {
+	pub fn value(self, value: Val) -> Result<()> {
 		self.binding(LazyBinding::Bound(LazyVal::new_resolved(value)))
 	}
-	pub fn bindable(self, bindable: TraceBox<dyn Bindable>) -> &'v mut ObjValueBuilder {
+	pub fn bindable(self, bindable: TraceBox<dyn Bindable>) -> Result<()> {
 		self.binding(LazyBinding::Bindable(Cc::new(bindable)))
 	}
-	pub fn binding(self, binding: LazyBinding) -> &'v mut ObjValueBuilder {
-		self.value.map.insert(
-			self.name,
+	pub fn binding(self, binding: LazyBinding) -> Result<()> {
+		let old = self.value.map.insert(
+			self.name.clone(),
 			ObjMember {
 				add: self.add,
 				visibility: self.visibility,
 				invoke: binding,
-				location: self.location,
+				location: self.location.clone(),
 			},
 		);
-		self.value
+		if old.is_some() {
+			push_frame(
+				CallLocation(self.location.as_ref()),
+				|| format!("field <{}> initializtion", self.name.clone()),
+				|| throw!(DuplicateFieldName(self.name.clone())),
+			)?
+		}
+		Ok(())
 	}
 }
--- a/crates/jrsonnet-macros/src/lib.rs
+++ b/crates/jrsonnet-macros/src/lib.rs
@@ -459,12 +459,12 @@
 			if self.is_option() {
 				quote! {
 					if let Some(value) = self.#ident {
-						out.member(#name.into()).value(value.try_into()?);
+						out.member(#name.into()).value(value.try_into()?)?;
 					}
 				}
 			} else {
 				quote! {
-					out.member(#name.into()).value(self.#ident.try_into()?);
+					out.member(#name.into()).value(self.#ident.try_into()?)?;
 				}
 			}
 		} else if self.is_option() {