diff --git a/src/parser3.h b/src/parser3.h
index b5a14ec..17cbc57 100644
--- a/src/parser3.h
+++ b/src/parser3.h
@@ -571,7 +571,7 @@ inline PRESERVE_NONE WeaselJsonStatus n_string2(Parser3 *self, char *buf,
             return WeaselJson_REJECT;
           }
           buf += 6;
-          assert(codepoint < 0x10ffff);
+          assert(codepoint <= 0x10ffff);
           self->writeBuf[3] = (0b00111111 & codepoint) | 0b10000000;
           codepoint >>= 6;
           self->writeBuf[2] = (0b00111111 & codepoint) | 0b10000000;