diff --git a/mozilla/webtools/bugzilla/bug_form.pl b/mozilla/webtools/bugzilla/bug_form.pl
index 0ce4f29bd48..af6618db5d8 100644
--- a/mozilla/webtools/bugzilla/bug_form.pl
+++ b/mozilla/webtools/bugzilla/bug_form.pl
@@ -496,7 +496,7 @@ if ($canedit || $::userid == $assignedtoid ||
         $knum++;
         print "<INPUT TYPE=radio NAME=knob VALUE=duplicate>
         Resolve bug, mark it as duplicate of bug # 
-        <INPUT NAME=dup_id SIZE=6 ONCHANGE=\"document.changeform.knob\[$knum\].checked=true\"><br>\n";
+        <INPUT NAME=dup_id SIZE=6 ONCHANGE=\"if (this.value != '') {document.changeform.knob\[$knum\].checked=true}\"><br>\n";
         $knum++;
         my $assign_element = "<INPUT NAME=\"assigned_to\" SIZE=32 ONCHANGE=\"if ((this.value != ".SqlQuote($bug{'assigned_to_email'}) .") && (this.value != '')) { document.changeform.knob\[$knum\].checked=true; }\" VALUE=\"$bug{'assigned_to_email'}\">";