diff --git a/starlark_import/unmarshal.go b/starlark_import/unmarshal.go
index 33c0cd9..b243471 100644
--- a/starlark_import/unmarshal.go
+++ b/starlark_import/unmarshal.go
@@ -34,6 +34,9 @@
 		return reflect.ValueOf(value), nil
 	}
 	zero := reflect.Zero(ty)
+	if value == nil {
+		panic("nil value")
+	}
 	var result reflect.Value
 	if ty.Kind() == reflect.Interface {
 		var err error