diff --git a/tests/HelpersTest.cpp b/tests/HelpersTest.cpp
index afbefc9a..694ebb07 100644
--- a/tests/HelpersTest.cpp
+++ b/tests/HelpersTest.cpp
@@ -1,5 +1,6 @@
 #include "app_helper.hpp"
 
+#include <climits>
 #include <complex>
 #include <cstdint>
 #include <cstdio>
@@ -553,8 +554,8 @@ TEST(Types, TypeName) {
 }
 
 TEST(Types, OverflowSmall) {
-    char x;
-    auto strmax = std::to_string(INT8_MAX + 1);
+    signed char x;
+    auto strmax = std::to_string(SCHAR_MAX + 1);
     EXPECT_FALSE(CLI::detail::lexical_cast(strmax, x));
 
     unsigned char y;
@@ -641,7 +642,7 @@ TEST(Types, LexicalCastParsable) {
 }
 
 TEST(Types, LexicalCastEnum) {
-    enum t1 : char { v1 = 5, v3 = 7, v5 = -9 };
+    enum t1 : signed char { v1 = 5, v3 = 7, v5 = -9 };
 
     t1 output;
     EXPECT_TRUE(CLI::detail::lexical_cast("-9", output));