diff --git a/loader.go b/loader.go
index 96cf45f..fc6336d 100644
--- a/loader.go
+++ b/loader.go
@@ -132,6 +132,9 @@ func flattenWithGrammar(prefix string, data map[string]any, out map[string]Messa
 				if gerund, ok := v["gerund"].(string); ok {
 					forms.Gerund = gerund
 				}
+				if forms.Past == "" || forms.Gerund == "" {
+					continue
+				}
 				grammar.Verbs[core.Lower(verbName)] = forms
 				continue
 			}
diff --git a/loader_test.go b/loader_test.go
index 2cfa9bc..c2d3d86 100644
--- a/loader_test.go
+++ b/loader_test.go
@@ -132,6 +132,12 @@ func TestFlattenWithGrammar(t *testing.T) {
 					"past":   "tested",
 					"gerund": "testing",
 				},
+				"partial_past": map[string]any{
+					"past": "partialed",
+				},
+				"partial_gerund": map[string]any{
+					"gerund": "partialing",
+				},
 				"publish_draft": map[string]any{
 					"base":   "publish",
 					"past":   "published",
@@ -201,6 +207,18 @@ func TestFlattenWithGrammar(t *testing.T) {
 	if _, ok := grammar.Verbs["publish_draft"]; ok {
 		t.Error("verb should be stored under explicit base, not JSON key")
 	}
+	if _, ok := grammar.Verbs["partial_past"]; ok {
+		t.Error("incomplete verb entry with only past should be skipped")
+	}
+	if _, ok := grammar.Verbs["partial_gerund"]; ok {
+		t.Error("incomplete verb entry with only gerund should be skipped")
+	}
+	if _, ok := messages["gram.verb.partial_past"]; ok {
+		t.Error("gram.verb.partial_past should not be flattened into messages")
+	}
+	if _, ok := messages["gram.verb.partial_gerund"]; ok {
+		t.Error("gram.verb.partial_gerund should not be flattened into messages")
+	}
 
 	// Noun extracted
 	if n, ok := grammar.Nouns["widget"]; !ok {