diff --git a/CHANGES.md b/CHANGES.md
index ee204c62..5c405c7e 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,6 @@
# Changes in HTMLDOC v1.9.17
+- Fixed multiple conversions of UTF-8 HTML files from the GUI (Issue #496)
- Fixed some minor CodeQL warnings.
diff --git a/doc/1-intro.html b/doc/1-intro.html
index 3c4419ae..48a4d2f4 100644
--- a/doc/1-intro.html
+++ b/doc/1-intro.html
@@ -2,7 +2,7 @@
-
+
HTMLDOC Users Manual
diff --git a/htmldoc/htmllib.cxx b/htmldoc/htmllib.cxx
index df753d02..dbb9503e 100644
--- a/htmldoc/htmllib.cxx
+++ b/htmldoc/htmllib.cxx
@@ -2510,6 +2510,8 @@ htmlSetCharSet(const char *cs) /* I - Character set file to load */
// bottom 128 characters matching US ASCII...
_htmlUTF8 = 0x80;
+ memset(_htmlCharacters, 0, sizeof(_htmlCharacters));
+
for (i = 0; i < 128; i ++)
{
/*