diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 6c30e6d54..a4efd397e 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -187,7 +187,7 @@ static void prim_typeOf(EvalState & state, const Pos & pos, Value * * args, Valu
         case tPrimOpApp:
             t = "lambda";
             break;
-	case tExternal:
+        case tExternal:
             t = args[0]->external->typeOf();
             break;
         default: abort();