diff --git a/src/client/windows/main.cpp b/src/client/windows/main.cpp
index 70876021..b8e211ae 100644
--- a/src/client/windows/main.cpp
+++ b/src/client/windows/main.cpp
@@ -9,6 +9,7 @@
 #include <WinSock2.h>
 #include <shellapi.h>
 #include <Shlobj.h>
+#include <cctype>
 
 // enable visual styles for message boxes
 #pragma comment(linker,"\"/manifestdependency:type='win32' name='Microsoft.Windows.Common-Controls' version='6.0.0.0' processorArchitecture='*' publicKeyToken='6595b64144ccf1df' language='*'\"")
diff --git a/src/config/string_iteration.h b/src/config/string_iteration.h
index f342c094..9233c613 100644
--- a/src/config/string_iteration.h
+++ b/src/config/string_iteration.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <string>
+#include <cctype>
 
 template<typename ForwardIt>
 bool skip(ForwardIt* it, ForwardIt end, const char* str) {
diff --git a/src/runtime/Stage.cpp b/src/runtime/Stage.cpp
index 7bd549c7..7be5e482 100644
--- a/src/runtime/Stage.cpp
+++ b/src/runtime/Stage.cpp
@@ -511,7 +511,7 @@ void Stage::finish_sequence(ConstKeySequenceRange sequence) {
   assert(sequence.begin() == m_sequence.begin());
   assert(sequence.size() <= m_sequence.size());
   auto length = sequence.size();
-  for (auto i = 0; i < length; ) {
+  for (auto i = size_t{ }; i < length; ) {
     const auto it = begin(m_sequence) + i;
     if (it->state == KeyState::Down || it->state == KeyState::DownMatched) {
       if (!contains(it, end(m_sequence), KeyEvent{ it->key, KeyState::Up })) {
diff --git a/src/server/windows/main.cpp b/src/server/windows/main.cpp
index c509f71b..f550bec9 100644
--- a/src/server/windows/main.cpp
+++ b/src/server/windows/main.cpp
@@ -131,7 +131,7 @@ namespace {
     g_sending_key = true;
     g_flush_scheduled = false;
 
-    auto i = 0;
+    auto i = size_t{ };
     for (; i < g_send_buffer.size(); ++i) {
       const auto& event = g_send_buffer[i];
       const auto is_first = (i == 0);