diff --git a/CMakeLists.txt b/CMakeLists.txt
index 34e6bed..0c163ab 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -34,7 +34,7 @@ if(CXXOPTS_USE_UNICODE_HELP)
   pkg_check_modules(ICU REQUIRED icu-uc)
 
   set(CXXOPTS_LINKER_LIBRARIES "${ICU_LIBRARIES}")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DCXXOPTS_USE_UNICODE")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -DCXXOPTS_USE_UNICODE")
 
 endif()
 
diff --git a/src/cxxopts.hpp b/src/cxxopts.hpp
index 91d3aa5..5bd7d5f 100644
--- a/src/cxxopts.hpp
+++ b/src/cxxopts.hpp
@@ -998,7 +998,7 @@ Options::parse(int& argc, char**& argv)
       {
         const std::string& s = result[4];
 
-        for (int i = 0; i != s.size(); ++i)
+        for (std::size_t i = 0; i != s.size(); ++i)
         {
           std::string name(1, s[i]);
           auto iter = m_options.find(name);