diff --git a/src/observe.ts b/src/observe.ts
index b6268e0a4..ea91d1966 100644
--- a/src/observe.ts
+++ b/src/observe.ts
@@ -27,6 +27,7 @@ export function observe<T>(
         options = reactionOrOptions;
     }
     let dispose: (() => void) | undefined;
+    let isFirstRun = true;
     const e: ObserveEventCallback<T> = { num: 0 };
     // Wrap it in a function so it doesn't pass all the arguments to run()
     const update = function () {
@@ -57,7 +58,7 @@ export function observe<T>(
         endBatch();
 
         // Call the reaction if there is one and the value changed
-        if (reaction && (e.num > 0 || !isEvent(selectorOrRun as any)) && e.previous !== e.value) {
+        if (reaction && (e.num > 0 || !isEvent(selectorOrRun as any)) && (isFirstRun || e.previous !== e.value)) {
             reaction(e);
         }
 
@@ -66,6 +67,8 @@ export function observe<T>(
 
         // Increment the counter
         e.num++;
+
+        isFirstRun = false;
     };
 
     update();
diff --git a/tests/computed.test.ts b/tests/computed.test.ts
index 31f0a44e2..6263e4d09 100644
--- a/tests/computed.test.ts
+++ b/tests/computed.test.ts
@@ -258,6 +258,19 @@ describe('Two way Computed', () => {
         expect(obs.test.get()).toEqual(true);
         expect(obs.test2.get()).toEqual(false);
     });
+    test('Computed activates when undefined', () => {
+        const obs = observable<boolean[]>(undefined);
+        const comp = computed(() => {
+            return obs.get()?.filter((a) => !!a);
+        });
+        let observed: boolean[];
+        observe(() => {
+            observed = comp.get();
+        });
+        expect(observed!).toEqual(undefined);
+        obs.set([]);
+        expect(observed!).toEqual([]);
+    });
     test('Two way computed value is set before calling setter', () => {
         const obs = observable(0);
 
diff --git a/tests/react.test.ts b/tests/react.test.ts
index 1f01ea350..6427d9823 100644
--- a/tests/react.test.ts
+++ b/tests/react.test.ts
@@ -647,7 +647,7 @@ describe('useObserve', () => {
         expect(num).toEqual(2);
         expect(numSets).toEqual(1);
     });
-    test('useObserve with undefined never calls reaction', () => {
+    test('useObserve with undefined calls reaction once', () => {
         let num = 0;
         let numSets = 0;
         function Test() {
@@ -664,8 +664,8 @@ describe('useObserve', () => {
         }
         render(createElement(App));
 
-        expect(num).toEqual(1);
-        expect(numSets).toEqual(0);
+        expect(num).toEqual(2);
+        expect(numSets).toEqual(1);
     });
 });