diff --git a/snix/eval/src/builtins/mod.rs b/snix/eval/src/builtins/mod.rs
index 13d1d3df7..a99a96571 100644
--- a/snix/eval/src/builtins/mod.rs
+++ b/snix/eval/src/builtins/mod.rs
@@ -150,7 +150,7 @@ mod pure_builtins {
         let xs = set.to_attrs()?;
         let mut output = Vec::with_capacity(xs.len());
 
-        for (key, _val) in xs.iter() {
+        for (key, _val) in xs.iter_sorted() {
             output.push(Value::from(key.clone()));
         }
 
@@ -162,7 +162,7 @@ mod pure_builtins {
         let xs = set.to_attrs()?;
         let mut output = Vec::with_capacity(xs.len());
 
-        for (_key, val) in xs.iter() {
+        for (_key, val) in xs.iter_sorted() {
             output.push(val.clone());
         }
 
@@ -789,13 +789,13 @@ mod pure_builtins {
         if left_set.is_empty() {
             return Ok(Value::attrs(NixAttrs::empty()));
         }
-        let mut left_keys = left_set.keys();
+        let mut left_keys = left_set.keys_sorted();
 
         let right_set = y.to_attrs()?;
         if right_set.is_empty() {
             return Ok(Value::attrs(NixAttrs::empty()));
         }
-        let mut right_keys = right_set.keys();
+        let mut right_keys = right_set.keys_sorted();
 
         let mut out: BTreeMap<NixString, Value> = BTreeMap::new();
 
diff --git a/snix/eval/src/builtins/to_xml.rs b/snix/eval/src/builtins/to_xml.rs
index c91841926..46a711a4c 100644
--- a/snix/eval/src/builtins/to_xml.rs
+++ b/snix/eval/src/builtins/to_xml.rs
@@ -67,7 +67,7 @@ fn value_variant_to_xml<W: Write>(w: &mut XmlEmitter<W>, value: &Value) -> Resul
         Value::Attrs(attrs) => {
             w.write_open_tag("attrs", &[])?;
 
-            for elem in attrs.iter() {
+            for elem in attrs.iter_sorted() {
                 w.write_open_tag("attr", &[("name", &elem.0.to_str_lossy())])?;
                 value_variant_to_xml(w, elem.1)?;
                 w.write_closing_tag("attr")?;
diff --git a/snix/eval/src/value/attrs.rs b/snix/eval/src/value/attrs.rs
index 363cf3b1d..8df69abd4 100644
--- a/snix/eval/src/value/attrs.rs
+++ b/snix/eval/src/value/attrs.rs
@@ -318,6 +318,12 @@ impl NixAttrs {
         })
     }
 
+    /// Same as [Self::keys], but marks call sites which rely on the
+    /// iteration being lexicographic.
+    pub fn keys_sorted(&self) -> Keys {
+        self.keys()
+    }
+
     /// Implement construction logic of an attribute set, to encapsulate
     /// logic about attribute set optimisations inside of this module.
     pub fn construct(