diff --git a/mock.go b/mock.go
index ffda2e7..cc8e064 100644
--- a/mock.go
+++ b/mock.go
@@ -480,17 +480,24 @@ func (m *mockTickerFunc) next() time.Time {
 
 func (m *mockTickerFunc) fire(_ time.Time) {
 	m.mock.mu.Lock()
-	defer m.mock.mu.Unlock()
-	if m.done || m.inProgress {
+	if m.done {
+		m.mock.mu.Unlock()
 		return
 	}
 	m.nxt = m.nxt.Add(m.d)
 	m.mock.recomputeNextLocked()
+	// we need this check to happen after we've computed the next tick,
+	// otherwise it will be immediately rescheduled.
+	if m.inProgress {
+		m.mock.mu.Unlock()
+		return
+	}
 
 	m.inProgress = true
 	m.mock.mu.Unlock()
 	err := m.f()
 	m.mock.mu.Lock()
+	defer m.mock.mu.Unlock()
 	m.inProgress = false
 	m.cond.Broadcast() // wake up anything waiting for f to finish
 	if err != nil {
diff --git a/mock_test.go b/mock_test.go
index 47316ca..8099738 100644
--- a/mock_test.go
+++ b/mock_test.go
@@ -292,9 +292,13 @@ func TestTickerFunc_LongCallback(t *testing.T) {
 	case <-testCtx.Done():
 		t.Fatal("timeout waiting for tickStart")
 	}
-	// second tick completes immediately, since it doesn't actually call the
-	// ticker function.
-	mClock.Advance(time.Second).MustWait(testCtx)
+	// additional ticks complete immediately.
+	elapsed := time.Duration(0)
+	for elapsed < 5*time.Second {
+		d, wt := mClock.AdvanceNext()
+		elapsed += d
+		wt.MustWait(testCtx)
+	}
 
 	waitErr := make(chan error, 1)
 	go func() {