diff --git a/CMakeLists.txt b/CMakeLists.txt
index 50fe4da4..cdffae6c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,6 +21,9 @@ if(MSVC)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /GR- /EHsc /utf-8 /O2")
 else()
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-rtti -fexceptions -O2")
+    if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -stdlib=libc++")
+    endif()
 endif()
 
 option(PK_EXPORT_C_API "Export C API" ON)
diff --git a/README.md b/README.md
index d74ee0ee..0d786043 100644
--- a/README.md
+++ b/README.md
@@ -41,6 +41,7 @@ To compile it with your project, these flags must be set:
 + `--std=c++17` flag must be set
 + Exception must be enabled
 + RTTI is not required
++ If clang is used, `-stdlib=libc++` must be set
 
 !!!
 For maximum performance, we recommend to use `clang++` with `-O2` flag.
diff --git a/docs/quick-start/installation.md b/docs/quick-start/installation.md
index 3de66c02..44d3e0ce 100644
--- a/docs/quick-start/installation.md
+++ b/docs/quick-start/installation.md
@@ -23,6 +23,7 @@ To compile it with your project, these flags must be set:
 + `--std=c++17` flag must be set
 + Exception must be enabled
 + RTTI is not required
++ If clang is used, `-stdlib=libc++` must be set
 
 ### Example
 
diff --git a/include/pocketpy/str.h b/include/pocketpy/str.h
index 7a191011..0291faba 100644
--- a/include/pocketpy/str.h
+++ b/include/pocketpy/str.h
@@ -163,27 +163,18 @@ inline bool is_unicode_Lo_char(uint32_t c) {
 
 struct StrName {
     uint16_t index;
-    StrName(): index(0) {}
-    explicit StrName(uint16_t index): index(index) {}
-    StrName(const char* s): index(get(s).index) {}
-    StrName(const Str& s){
-        index = get(s.sv()).index;
-    }
-    std::string_view sv() const { return _r_interned[index-1].sv(); }
+    StrName();
+    explicit StrName(uint16_t index);
+    StrName(const char* s);
+    StrName(const Str& s);
+    std::string_view sv() const;
     bool empty() const { return index == 0; }
 
     friend std::ostream& operator<<(std::ostream& os, const StrName& sn){
         return os << sn.sv();
     }
 
-    static bool is_valid(int index) {
-        // check _r_interned[index-1] is valid
-        return index > 0 && index <= _r_interned.size();
-    }
-
-    Str escape() const {
-        return _r_interned[index-1].escape();
-    }
+    Str escape() const;
 
     bool operator==(const StrName& other) const noexcept {
         return this->index == other.index;
@@ -204,14 +195,8 @@ struct StrName {
     inline static std::map<Str, uint16_t, std::less<>> _interned;
     inline static std::vector<Str> _r_interned;
 
-    static StrName get(std::string_view s){
-        auto it = _interned.find(s);
-        if(it != _interned.end()) return StrName(it->second);
-        uint16_t index = (uint16_t)(_r_interned.size() + 1);
-        _interned[s] = index;
-        _r_interned.push_back(s);
-        return StrName(index);
-    }
+    static bool is_valid(int index);
+    static StrName get(std::string_view s);
 };
 
 struct FastStrStream{
diff --git a/src/pocketpy.cpp b/src/pocketpy.cpp
index 5a46b0af..b9d368a9 100644
--- a/src/pocketpy.cpp
+++ b/src/pocketpy.cpp
@@ -145,10 +145,10 @@ void init_builtins(VM* _vm) {
 
     _vm->bind_builtin_func<1>("__import__", [](VM* vm, ArgsView args) {
         const Str& name = CAST(Str&, args[0]);
-        auto dot = name.sv().find_first_of(".");
+        auto dot = name.sv().find_last_of(".");
         if(dot != std::string_view::npos){
             auto ext = name.sv().substr(dot);
-            if(ext == ".so" || ext == ".dll" || ext == ".dylib" || ext == ".pyd"){
+            if(ext == ".so" || ext == ".dll" || ext == ".dylib"){
                 dylib_entry_t entry = load_dylib(name.c_str());
                 if(!entry){
                     vm->_error("ImportError", "cannot load dynamic library: " + name.escape());
diff --git a/src/str.cpp b/src/str.cpp
index 35cb1f2b..68357643 100644
--- a/src/str.cpp
+++ b/src/str.cpp
@@ -239,4 +239,31 @@ namespace pkpy {
     int Str::u8_length() const {
         return _byte_index_to_unicode(size);
     }
+
+    StrName StrName::get(std::string_view s){
+        auto it = _interned.find(s);
+        if(it != _interned.end()) return StrName(it->second);
+        uint16_t index = (uint16_t)(_r_interned.size() + 1);
+        _interned[s] = index;
+        _r_interned.push_back(s);
+        return StrName(index);
+    }
+
+    Str StrName::escape() const {
+        return _r_interned[index-1].escape();
+    }
+
+    bool StrName::is_valid(int index) {
+        // check _r_interned[index-1] is valid
+        return index > 0 && index <= _r_interned.size();
+    }
+
+    StrName::StrName(): index(0) {}
+    StrName::StrName(uint16_t index): index(index) {}
+    StrName::StrName(const char* s): index(get(s).index) {}
+    StrName::StrName(const Str& s){
+        index = get(s.sv()).index;
+    }
+
+    std::string_view StrName::sv() const { return _r_interned[index-1].sv(); }
 } // namespace pkpy
\ No newline at end of file
diff --git a/tests/dylib/build.sh b/tests/dylib/build.sh
index 5fd6f97e..9a38f299 100644
--- a/tests/dylib/build.sh
+++ b/tests/dylib/build.sh
@@ -1,2 +1 @@
-SRC=$(find ../../src/ -name "*.cpp")
 clang++ -std=c++17 -fno-rtti -O2 -stdlib=libc++ -Wfatal-errors -o libtest.so test.cpp -I../../include -fPIC -shared
\ No newline at end of file