diff --git a/include/cxxopts.hpp b/include/cxxopts.hpp
index 1644692..6e9a61e 100644
--- a/include/cxxopts.hpp
+++ b/include/cxxopts.hpp
@@ -39,6 +39,10 @@ THE SOFTWARE.
 #include <unordered_set>
 #include <vector>
 
+#ifdef __sun
+#define int8_t signed char
+#endif
+
 #ifdef __cpp_lib_optional
 #include <optional>
 #define CXXOPTS_HAS_OPTIONAL