diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 6ea6255d..c6f18ac4 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -46,6 +46,8 @@ jobs:
       run: python3 scripts/run_tests.py
     - name: Benchmark
       run: python3 scripts/run_tests.py benchmark
+    - name: GCC Build Test
+      run: g++ -o pocketpy --std=c++17 src/main.cpp
   build_macos:
       runs-on: macos-latest
       steps:
diff --git a/src/io.h b/src/io.h
index 2ae87595..b93803eb 100644
--- a/src/io.h
+++ b/src/io.h
@@ -31,16 +31,16 @@ struct FileIO {
     bool is_text() const { return mode != "rb" && mode != "wb" && mode != "ab"; }
 
     FileIO(VM* vm, Str file, Str mode): file(file), mode(mode) {
-        std::ios_base::openmode extra = 0;
+        std::ios_base::openmode extra = static_cast<std::ios_base::openmode>(0);
         if(mode == "rb" || mode == "wb" || mode == "ab"){
             extra |= std::ios::binary;
         }
         if(mode == "rt" || mode == "r" || mode == "rb"){
-            _fs.open(file.sv(), std::ios::in | extra);
+            _fs.open(file.str(), std::ios::in | extra);
         }else if(mode == "wt" || mode == "w" || mode == "wb"){
-            _fs.open(file.sv(), std::ios::out | extra);
+            _fs.open(file.str(), std::ios::out | extra);
         }else if(mode == "at" || mode == "a" || mode == "ab"){
-            _fs.open(file.sv(), std::ios::app | extra);
+            _fs.open(file.str(), std::ios::app | extra);
         }else{
             vm->ValueError("invalid mode");
         }