diff --git a/src/font.cpp b/src/font.cpp
index 667e098b0b2..134a6dd8f1b 100644
--- a/src/font.cpp
+++ b/src/font.cpp
@@ -955,7 +955,7 @@ std::string word_wrap_text(const std::string& unwrapped_text, int font_size, int
 	while(1) {
 		if(start_of_line) {
 			format_string = "";
-			while(ch != end && *ch < 0x100 && is_format_char(*ch)) {
+			while(ch != end && *ch < 0x100U && is_format_char(*ch)) {
 				format_string.append(ch.substr().first, ch.substr().second);
 				++ch;
 			}