diff --git a/ConflictSet.cpp b/ConflictSet.cpp
index 88792d2..7a0d10d 100644
--- a/ConflictSet.cpp
+++ b/ConflictSet.cpp
@@ -1137,7 +1137,7 @@ std::string getPartialKeyPrintable(Node *n) {
 std::string strinc(std::string_view str, bool &ok) {
   int index;
   for (index = str.size() - 1; index >= 0; index--)
-    if (str[index] != 255)
+    if ((uint8_t &)(str[index]) != 255)
       break;
 
   // Must not be called with a string that consists only of zero or more '\xff'