diff --git a/loader.go b/loader.go
index dfebee2..cacde28 100644
--- a/loader.go
+++ b/loader.go
@@ -351,13 +351,49 @@ func loadSignalPriors(grammar *GrammarData, priors map[string]any) {
 			grammar.Signals.Priors[key] = make(map[string]float64, len(bucket))
 		}
 		for role, value := range bucket {
-			if score := toFloat64(value); score != 0 {
-				grammar.Signals.Priors[key][core.Lower(role)] = score
+			score, ok := float64Value(value)
+			if !ok {
+				continue
 			}
+			grammar.Signals.Priors[key][core.Lower(role)] = score
 		}
 	}
 }
 
+func float64Value(v any) (float64, bool) {
+	if v == nil {
+		return 0, false
+	}
+	switch n := v.(type) {
+	case float64:
+		return n, true
+	case float32:
+		return float64(n), true
+	case int:
+		return float64(n), true
+	case int64:
+		return float64(n), true
+	case int32:
+		return float64(n), true
+	case int16:
+		return float64(n), true
+	case int8:
+		return float64(n), true
+	case uint:
+		return float64(n), true
+	case uint64:
+		return float64(n), true
+	case uint32:
+		return float64(n), true
+	case uint16:
+		return float64(n), true
+	case uint8:
+		return float64(n), true
+	default:
+		return 0, false
+	}
+}
+
 func shouldSkipDeprecatedEnglishGrammarEntry(fullKey string) bool {
 	switch fullKey {
 	case "gram.noun.passed", "gram.noun.failed", "gram.noun.skipped",
diff --git a/loader_test.go b/loader_test.go
index 2f6e842..8007ebc 100644
--- a/loader_test.go
+++ b/loader_test.go
@@ -624,3 +624,38 @@ func TestCustomFSLoader(t *testing.T) {
 		t.Errorf("signal priors not loaded correctly: %+v", gd.Signals.Priors["draft"])
 	}
 }
+
+func TestCustomFSLoaderPreservesZeroSignalPriors(t *testing.T) {
+	fs := fstest.MapFS{
+		"locales/test.json": &fstest.MapFile{
+			Data: []byte(`{
+				"gram": {
+					"signal": {
+						"prior": {
+							"commit": { "verb": 0, "noun": 1 }
+						}
+					}
+				}
+			}`),
+		},
+	}
+
+	loader := NewFSLoader(fs, "locales")
+	_, grammar, err := loader.Load("test")
+	if err != nil {
+		t.Fatalf("Load(test) failed: %v", err)
+	}
+	if grammar == nil {
+		t.Fatal("expected grammar data")
+	}
+	bucket, ok := grammar.Signals.Priors["commit"]
+	if !ok {
+		t.Fatal("signal priors for commit were not loaded")
+	}
+	if got := bucket["verb"]; got != 0 {
+		t.Fatalf("signal priors verb = %v, want 0", got)
+	}
+	if got := bucket["noun"]; got != 1 {
+		t.Fatalf("signal priors noun = %v, want 1", got)
+	}
+}