diff --git a/gui/ThemeEngine.cpp b/gui/ThemeEngine.cpp
index 2f9c7ae2794..e063e11674d 100644
--- a/gui/ThemeEngine.cpp
+++ b/gui/ThemeEngine.cpp
@@ -1503,7 +1503,7 @@ Common::String ThemeEngine::genLocalizedFontFilename(const Common::String &filen
 
 bool ThemeEngine::themeConfigParseHeader(Common::String header, Common::String &themeName) {
 	// Check that header is not corrupted
-	if (header[0] < 0 || header[0] > 127) {
+	if ((byte)header[0] > 127) {
 		warning("Corrupted theme header found");
 		return false;
 	}