diff --git a/pipeline.go b/pipeline.go
index 2f71cd3..f452c8e 100644
--- a/pipeline.go
+++ b/pipeline.go
@@ -79,7 +79,11 @@ func CompareVariants(r *Responsive, ctx *Context) map[string]float64 {
 	scores := make(map[string]float64)
 	for i := range len(imprints) {
 		for j := i + 1; j < len(imprints); j++ {
-			key := imprints[i].name + ":" + imprints[j].name
+			left, right := imprints[i].name, imprints[j].name
+			if right < left {
+				left, right = right, left
+			}
+			key := left + ":" + right
 			scores[key] = imprints[i].imp.Similar(imprints[j].imp)
 		}
 	}
diff --git a/pipeline_test.go b/pipeline_test.go
index 4061a93..d6637b3 100644
--- a/pipeline_test.go
+++ b/pipeline_test.go
@@ -142,6 +142,25 @@ func TestCompareVariants(t *testing.T) {
 	}
 }
 
+func TestCompareVariants_CanonicalKeyOrder(t *testing.T) {
+	svc, _ := i18n.New()
+	i18n.SetDefault(svc)
+	ctx := NewContext()
+
+	r := NewResponsive().
+		Variant("mobile", NewLayout("C").C(El("p", Text("Hello")))).
+		Variant("desktop", NewLayout("C").C(El("p", Text("Hello"))))
+
+	scores := CompareVariants(r, ctx)
+
+	if _, ok := scores["desktop:mobile"]; !ok {
+		t.Fatalf("CompareVariants should canonicalise pair keys, got %v", scores)
+	}
+	if _, ok := scores["mobile:desktop"]; ok {
+		t.Fatalf("CompareVariants should not emit reversed duplicate keys, got %v", scores)
+	}
+}
+
 func TestCompareVariants_NilResponsive(t *testing.T) {
 	scores := CompareVariants(nil, NewContext())
 	if len(scores) != 0 {