diff --git a/core/fpdfapi/font/fpdf_font_cid.cpp b/core/fpdfapi/font/fpdf_font_cid.cpp
index e451546..dd37551 100644
--- a/core/fpdfapi/font/fpdf_font_cid.cpp
+++ b/core/fpdfapi/font/fpdf_font_cid.cpp
@@ -687,7 +687,7 @@
           iSize = 1;
         str[iSize - 1] = (uint8_t)charcode;
         if (iSize > 1)
-          memset(str + 1, 0, iSize - 1);
+          memset(str, 0, iSize - 1);
         return iSize;
       }
       if (charcode < 0x10000) {