diff --git a/bau/bau.js b/bau/bau.js
index 39560ae0..bd72fbbe 100644
--- a/bau/bau.js
+++ b/bau/bau.js
@@ -52,6 +52,7 @@ export default function Bau(input) {
   let updateDom = (state, op) => {
     !_stateOps.length && _window.requestAnimationFrame(processDom);
     _stateOps.push([state, op]);
+    for (let l of state.listeners) l.state.dirty = true;
   };
 
   const processDom = () => {
@@ -249,10 +250,14 @@ export default function Bau(input) {
     rawVal: initVal,
     bindings: [],
     listeners: [],
+    dirty: false,
     __isState: true,
     get val() {
       let _state = this;
       _curDeps?.g?.add(_state);
+      if (_state.computed && _state.dirty) {
+        deriveInternal(_state.computed, _state);
+      }
       return (
         _state.valProxy ??
         ((_state.valProxy = isArrayOrObject(initVal)
@@ -304,12 +309,13 @@ export default function Bau(input) {
       )
     ))
       dep.listeners.push(listener);
+      state.dirty = false;
   };
 
   let derive = (computed, options) => {
     let state = createState(undefined, options);
+    state.computed = computed;
     deriveInternal(computed, state);
-    state.computed = true;
     return state;
   };
 
diff --git a/bau/test/derive.test.js b/bau/test/derive.test.js
index 66a77056..f686792e 100644
--- a/bau/test/derive.test.js
+++ b/bau/test/derive.test.js
@@ -115,4 +115,55 @@ describe("derive", async () => {
     assert.equal(b.val, 1);
     expect(spys).toHaveBeenCalledTimes(2);
   });
+
+  it("updates incrementally", () => {
+    const a = bau.state(false);
+    const b = bau.state(false);
+    const derived = bau.derive(() => {
+      if (!a.val) return 1;
+      if (!b.val) return 2;
+      return 3;
+    });
+
+    assert.equal(derived.val, 1);
+    a.val = true;
+    assert.equal(derived.val, 2);
+    b.val = true;
+    assert.equal(derived.val, 3);
+  });
+
+  it("updates when first null", () => {
+    const a = bau.state(false);
+    const b = bau.state(false);
+    const derived = bau.derive(() => {
+      if (!a.val) return null;
+      if (!b.val) return null;
+      return true;
+    });
+
+    assert.equal(derived.val, null);
+    a.val = true;
+    b.val = true;
+    assert.equal(derived.val, true);
+  });
+
+  it("does not call derive when non-dependencies change", () => {
+    const a = bau.state(0);
+    const b = bau.state(0);
+    let called = 0;
+    const derived = bau.derive(() => {
+      ++called;
+      return a.val;
+    });
+    assert.equal(derived.val, 0);
+    assert.equal(derived.val, 0);
+    assert.equal(called, 1);
+    ++a.val;
+    assert.equal(derived.val, 1);
+    assert.equal(derived.val, 1);
+    assert.equal(called, 2);
+    ++b.val;
+    assert.equal(derived.val, 1);
+    assert.equal(called, 2);
+  });
 });