diff --git a/bootstrap/typecheck.cc b/bootstrap/typecheck.cc
index a4f7175..f7b4cb3 100644
--- a/bootstrap/typecheck.cc
+++ b/bootstrap/typecheck.cc
@@ -70,28 +70,29 @@ std::any TypeCheckVisitor::visitFactor(xlangParser::FactorContext *ctx) {
     auto token = identifier->getSymbol();
     auto name = token->getText();
     if (ctx->LeftParen()) {
-      if (function_arity.find(name) == function_arity.end()) {
+      if (function_arity.find(name) != function_arity.end()) {
+        if (auto expr_list = ctx->exprList()) {
+          auto arity = function_arity[name];
+          auto arg_num = expr_list->expr().size();
+          if (arity != arg_num) {
+            errorlistener.typeError(
+                token->getLine(), token->getCharPositionInLine(),
+                "function '" + name + "' expects " + std::to_string(arity) +
+                    " arguments, but got " + std::to_string(arg_num));
+          }
+        } else {
+          if (auto arity = function_arity[name]) {
+            errorlistener.typeError(
+                token->getLine(), token->getCharPositionInLine(),
+                "function '" + name + "' expects " + std::to_string(arity) +
+                    " arguments, but got none");
+          }
+        }
+      } else {
         errorlistener.typeError(token->getLine(),
                                 token->getCharPositionInLine(),
                                 "unknown function '" + name + "'");
       }
-      if (auto expr_list = ctx->exprList()) {
-        auto arity = function_arity[name];
-        auto arg_num = expr_list->expr().size();
-        if (arity != arg_num) {
-          errorlistener.typeError(
-              token->getLine(), token->getCharPositionInLine(),
-              "function '" + name + "' expects " + std::to_string(arity) +
-                  " arguments, but got " + std::to_string(arg_num));
-        }
-      } else {
-        if (auto arity = function_arity[name]) {
-          errorlistener.typeError(
-              token->getLine(), token->getCharPositionInLine(),
-              "function '" + name + "' expects " + std::to_string(arity) +
-                  " arguments, but got none");
-        }
-      }
       visitChildren(ctx);
     } else {
       if (!inScope(name)) {