diff --git a/cmd/mesh-controller/conditions_test.go b/cmd/mesh-controller/conditions_test.go
index 6e33426d..35bdefe2 100644
--- a/cmd/mesh-controller/conditions_test.go
+++ b/cmd/mesh-controller/conditions_test.go
@@ -86,7 +86,7 @@ func TestASilenceThroughTheVerbHoldsAndTheConditionStaysOpen(t *testing.T) {
 func TestUnreadableConditionsAreNotAWellMesh(t *testing.T) {
 	open := aMesh(t)
 	_, store := withConditionsInMemory(t)
-	store.Fail = errors.New("the bus is away")
+	store.SetFail(errors.New("the bus is away"))
 	asked, err := theThreeQuestions(t.Context(), open)
 	if err != nil {
 		t.Fatal(err)
@@ -98,7 +98,7 @@ func TestUnreadableConditionsAreNotAWellMesh(t *testing.T) {
 	if !strings.HasPrefix(said, "the open conditions could NOT be read") || strings.Contains(said, "no open conditions") {
 		t.Fatalf("%s", said)
 	}
-	store.Fail = nil
+	store.SetFail(nil)
 	asked, _ = theThreeQuestions(t.Context(), open)
 	said = printed(t, func() error { return printStatus(asked) })
 	if asked.well() && !strings.Contains(said, "no open conditions;") {
diff --git a/internal/conditions/memory.go b/internal/conditions/memory.go
index 1e23ee25..61134461 100644
--- a/internal/conditions/memory.go
+++ b/internal/conditions/memory.go
@@ -61,6 +61,14 @@ func (m *InMemory) Update(_ context.Context, key string, value []byte, revision
 	return nil
 }
 
+// SetFail makes every call fail with err from now on, or none with nil: under the store's lock, so a test may
+// change it while the keeper's own goroutine is telling.
+func (m *InMemory) SetFail(err error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.Fail = err
+}
+
 func (m *InMemory) Delete(_ context.Context, key string, revision uint64) error {
 	m.mu.Lock()
 	defer m.mu.Unlock()
diff --git a/internal/conditions/store_test.go b/internal/conditions/store_test.go
index 2d571abe..47d1e494 100644
--- a/internal/conditions/store_test.go
+++ b/internal/conditions/store_test.go
@@ -199,15 +199,17 @@ func TestAnUnreadableStoreClearsNothing(t *testing.T) {
 	if _, err := k.Observe(ctx, silent("ace")); err != nil {
 		t.Fatal(err)
 	}
-	store.Fail = errors.New("the bus is away")
+	store.SetFail(errors.New("the bus is away"))
 	if err := k.Reconcile(ctx, "S1", nil); err == nil {
 		t.Fatal("reconciled against a store it could not read")
 	}
 	if _, err := k.Open(ctx); err == nil {
 		t.Fatal("an unreadable store answered as read")
 	}
-	store.Fail = nil
+	store.SetFail(nil)
+	store.mu.Lock()
 	store.values["machine.g14.silent"] = Entry{Value: []byte("{not a condition"), Revision: 99}
+	store.mu.Unlock()
 	if _, err := k.Open(ctx); err == nil || !strings.Contains(err.Error(), "machine.g14.silent") {
 		t.Fatalf("an unreadable condition was left out rather than said: %v", err)
 	}