diff --git a/CHANGES.md b/CHANGES.md
index 185c27e..be5d0f6 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -13,6 +13,7 @@ v1.6.2 - YYYY-MM-DD
 - Fixed xref reconstruction for objects lacking a `Type` value.
 - Fixed `pdfioPageOpenStream` for indirect `Contents` arrays.
 - Fixed an error propagation bug when reading too-long values (Issue #146)
+- Fixed a bug when converting Unicode characters above plane 0 (issue #159)
 - Fixed a Clang warning.
 
 
diff --git a/pdfio-string.c b/pdfio-string.c
index 8790bc4..ecab0d6 100644
--- a/pdfio-string.c
+++ b/pdfio-string.c
@@ -229,7 +229,7 @@ _pdfio_utf16cpy(
     else
     {
       // 4-byte UTF-8
-      *dstptr++ = (char)(0xe0 | (ch >> 18));
+      *dstptr++ = (char)(0xf0 | (ch >> 18));
       *dstptr++ = (char)(0x80 | ((ch >> 12) & 0x3f));
       *dstptr++ = (char)(0x80 | ((ch >> 6) & 0x3f));
       *dstptr++ = (char)(0x80 | (ch & 0x3f));