diff --git a/src/parser3.h b/src/parser3.h
index 368efa5..37f9a64 100644
--- a/src/parser3.h
+++ b/src/parser3.h
@@ -644,7 +644,7 @@ inline Status t_hex3(Parser3 *self) {
   // Write codepoint in utf-8 if there's room in the user provided buffer. If
   // there's not room, flush, write into a temp buffer, and flush again.
   char tmp[4];
-  assert(self->utf8Codepoint < 0x10000);
+  assert(self->utf8Codepoint >= 0x10000);
   if (self->utf8Codepoint > 0x10FFFF) {
     return S_REJECT;
   }