--- a/crates/jrsonnet-stdlib/src/lib.rs
+++ b/crates/jrsonnet-stdlib/src/lib.rs
@@ -175,6 +175,7 @@
 		// Sets
 		("setMember", builtin_set_member::INST),
 		("setInter", builtin_set_inter::INST),
+		("setDiff", builtin_set_diff::INST),
 		// Compat
 		("__compare", builtin___compare::INST),
 	]
--- a/crates/jrsonnet-stdlib/src/sets.rs
+++ b/crates/jrsonnet-stdlib/src/sets.rs
@@ -71,3 +71,48 @@
 	}
 	Ok(ArrValue::lazy(out))
 }
+#[builtin]
+#[allow(non_snake_case, clippy::redundant_closure)]
+pub fn builtin_set_diff(a: ArrValue, b: ArrValue, keyF: Option<FuncVal>) -> Result<ArrValue> {
+	let mut a = a.iter_lazy();
+	let mut b = b.iter_lazy();
+
+	let keyF = keyF
+		.unwrap_or(FuncVal::identity())
+		.into_native::<((Thunk<Val>,), Val)>();
+	let keyF = |v| keyF(v);
+
+	let mut av = a.next();
+	let mut bv = b.next();
+	let mut ak = av.clone().map(keyF).transpose()?;
+	let mut bk = bv.map(keyF).transpose()?;
+
+	let mut out = Vec::new();
+	while let (Some(ac), Some(bc)) = (&ak, &bk) {
+		match evaluate_compare_op(ac, bc, BinaryOpType::Lt)? {
+			Ordering::Less => {
+				// In a, but not in b
+				out.push(av.clone().expect("ak != None"));
+				av = a.next();
+				ak = av.clone().map(keyF).transpose()?;
+			}
+			Ordering::Greater => {
+				bv = b.next();
+				bk = bv.map(keyF).transpose()?;
+			}
+			Ordering::Equal => {
+				av = a.next();
+				ak = av.clone().map(keyF).transpose()?;
+				bv = b.next();
+				bk = bv.map(keyF).transpose()?;
+			}
+		};
+	}
+	while let Some(ac) = &ak {
+		// In a, but not in b
+		out.push(av.clone().expect("ak != None"));
+		av = a.next();
+		ak = av.clone().map(keyF).transpose()?;
+	}
+	Ok(ArrValue::lazy(out))
+}
--- a/crates/jrsonnet-stdlib/src/std.jsonnet
+++ b/crates/jrsonnet-stdlib/src/std.jsonnet
@@ -214,21 +214,6 @@
           aux(a, b, i, j + 1, acc + [b[j]]) tailstrict;
     aux(a, b, 0, 0, []),
 
-  setDiff(a, b, keyF=id)::
-    local aux(a, b, i, j, acc) =
-      if i >= std.length(a) then
-        acc
-      else if j >= std.length(b) then
-        acc + a[i:]
-      else
-        if keyF(a[i]) == keyF(b[j]) then
-          aux(a, b, i + 1, j + 1, acc) tailstrict
-        else if keyF(a[i]) < keyF(b[j]) then
-          aux(a, b, i + 1, j, acc + [a[i]]) tailstrict
-        else
-          aux(a, b, i, j + 1, acc) tailstrict;
-    aux(a, b, 0, 0, []) tailstrict,
-
   mergePatch(target, patch)::
     if std.isObject(patch) then
       local target_object =