diff --git a/src/basic/utf8.h b/src/basic/utf8.h
index f5e9f8cacb..63991bf8c8 100644
--- a/src/basic/utf8.h
+++ b/src/basic/utf8.h
@@ -31,15 +31,15 @@ int utf8_encoded_valid_unichar(const char *str);
 int utf8_encoded_to_unichar(const char *str, char32_t *ret_unichar);
 
 static inline bool utf16_is_surrogate(char16_t c) {
-        return (0xd800 <= c && c <= 0xdfff);
+        return c >= 0xd800U && c <= 0xdfffU;
 }
 
 static inline bool utf16_is_trailing_surrogate(char16_t c) {
-        return (0xdc00 <= c && c <= 0xdfff);
+        return c >= 0xdc00U && c <= 0xdfffU;
 }
 
 static inline char32_t utf16_surrogate_pair_to_unichar(char16_t lead, char16_t trail) {
-                return ((lead - 0xd800) << 10) + (trail - 0xdc00) + 0x10000;
+        return ((((char32_t) lead - 0xd800U) << 10) + ((char32_t) trail - 0xdc00U) + 0x10000U);
 }
 
 size_t utf8_n_codepoints(const char *str);