diff --git a/include/ProgramOptions.hxx b/include/ProgramOptions.hxx
index 716f293..0555816 100644
--- a/include/ProgramOptions.hxx
+++ b/include/ProgramOptions.hxx
@@ -254,7 +254,9 @@ namespace po {
 	inline bool case_insensitive_eq(char x, char y) {
 		if(x == y)
 			return true;
+#ifndef __CHAR_UNSIGNED__
 		if(x >= 0 && y >= 0)
+#endif
 			if(std::tolower(x) == std::tolower(y))
 				return true;
 		return false;