diff --git a/src/Limonp/CodeConverter.hpp b/src/Limonp/CodeConverter.hpp
index 6806368..8831752 100644
--- a/src/Limonp/CodeConverter.hpp
+++ b/src/Limonp/CodeConverter.hpp
@@ -28,7 +28,7 @@ namespace Limonp
                 to.resize(from_size * 2); // iconv failed, may be you can raise this 2 to bigger number.
                 char * pto = (char*)to.c_str();
                 size_t to_size = to.size();
-                if(-1 == iconv(_iconv_handle, &pfrom, &from_size, &pto, &to_size))
+                if(size_t(-1) == iconv(_iconv_handle, &pfrom, &from_size, &pto, &to_size))
                 {
                     to.clear();
                     return false;
diff --git a/src/Limonp/Logger.hpp b/src/Limonp/Logger.hpp
index 28dd837..a26d480 100644
--- a/src/Limonp/Logger.hpp
+++ b/src/Limonp/Logger.hpp
@@ -49,7 +49,7 @@ namespace Limonp
 #ifdef LOGGER_LEVEL
                 if(level < LOGGER_LEVEL) return;
 #endif
-                size_t size = 256;
+                int size = 256;
                 string msg;
                 va_list ap;
                 while (1) {
diff --git a/src/Limonp/StringUtil.hpp b/src/Limonp/StringUtil.hpp
index 35b6a9e..a10a80e 100644
--- a/src/Limonp/StringUtil.hpp
+++ b/src/Limonp/StringUtil.hpp
@@ -29,7 +29,7 @@ namespace Limonp
 
     inline void string_format(string& res, const char* fmt, ...)
     {
-        size_t size = 256;
+        int size = 256;
         va_list ap;
         res.clear();
         while (1) {
@@ -49,7 +49,7 @@ namespace Limonp
     }
     inline string string_format(const char* fmt, ...) 
     {
-        size_t size = 256;
+        int size = 256;
         std::string str;
         va_list ap;
         while (1) {