diff --git a/.clang-tidy b/.clang-tidy
index b88a3d36..725db88e 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -49,7 +49,6 @@ Checks: >
         -readability-use-concise-preprocessor-directives,
         -readability-uppercase-literal-suffix,
         -performance-avoid-endl,
-        -performance-enum-size,
         -performance-inefficient-string-concatenation,
         -performance-no-automatic-move,
         -performance-noexcept-move-constructor
diff --git a/simplecpp.cpp b/simplecpp.cpp
index d37c0aa7..ea33fd14 100644
--- a/simplecpp.cpp
+++ b/simplecpp.cpp
@@ -24,6 +24,7 @@
 #include <cctype>
 #include <climits>
 #include <cstddef> // IWYU pragma: keep
+#include <cstdint>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
@@ -3366,7 +3367,7 @@ void simplecpp::preprocess(simplecpp::TokenList &output, const simplecpp::TokenL
     // True => code in current #if block should be kept
     // ElseIsTrue => code in current #if block should be dropped. the code in the #else should be kept.
     // AlwaysFalse => drop all code in #if and #else
-    enum IfState { True, ElseIsTrue, AlwaysFalse };
+    enum IfState : std::uint8_t { True, ElseIsTrue, AlwaysFalse };
     std::stack<int> ifstates;
     std::stack<const Token *> iftokens;
     ifstates.push(True);
diff --git a/simplecpp.h b/simplecpp.h
index 78609af3..da859cba 100644
--- a/simplecpp.h
+++ b/simplecpp.h
@@ -7,6 +7,7 @@
 #define simplecppH
 
 #include <cctype>
+#include <cstdint>
 #include <cstring>
 #include <iosfwd>
 #include <list>
@@ -39,9 +40,7 @@
 #  define SIMPLECPP_LIB
 #endif
 
-#ifdef _WIN32
-#  include <cstdint>
-#else
+#ifndef _WIN32
 #  include <sys/stat.h>
 #endif
 
@@ -63,10 +62,10 @@
 
 namespace simplecpp {
     /** C code standard */
-    enum cstd_t { CUnknown=-1, C89, C99, C11, C17, C23, C2Y };
+    enum cstd_t : std::int8_t { CUnknown=-1, C89, C99, C11, C17, C23, C2Y };
 
     /** C++ code standard */
-    enum cppstd_t { CPPUnknown=-1, CPP03, CPP11, CPP14, CPP17, CPP20, CPP23, CPP26 };
+    enum cppstd_t : std::int8_t { CPPUnknown=-1, CPP03, CPP11, CPP14, CPP17, CPP20, CPP23, CPP26 };
 
     using TokenString = std::string;
     class Macro;
@@ -204,7 +203,7 @@ namespace simplecpp {
     /** Output from preprocessor */
     struct SIMPLECPP_LIB Output {
         explicit Output(const std::vector<std::string> &files) : type(ERROR), location(files) {}
-        enum Type {
+        enum Type : std::uint8_t {
             ERROR, /* #error */
             WARNING, /* #warning */
             MISSING_HEADER,