diff --git a/src/frontends/qt4/GuiPrefs.cpp b/src/frontends/qt4/GuiPrefs.cpp
index ffbc524230..716014d167 100644
--- a/src/frontends/qt4/GuiPrefs.cpp
+++ b/src/frontends/qt4/GuiPrefs.cpp
@@ -1704,8 +1704,17 @@ void PrefFileformats::on_shortcutED_textEdited(const QString & s)
 void PrefFileformats::on_formatED_editingFinished()
 {
 	string const newname = fromqstr(formatED->displayText());
-	if (newname == currentFormat().name())
+	string const oldname = currentFormat().name();
+	if (newname == oldname)
 		return;
+	if (form_->converters().formatIsUsed(oldname)) {
+		Alert::error(_("Format in use"),
+			     _("You cannot change a format's short name "
+			       "if the format is used by a converter. "
+			       "Please remove the converter first."));
+		updateView();
+		return;
+	}
 
 	currentFormat().setName(newname);
 	changed();
diff --git a/status.16x b/status.16x
index 7cbc04d8fd..654a52f15e 100644
--- a/status.16x
+++ b/status.16x
@@ -70,6 +70,9 @@ What's new
 
 * USER INTERFACE
 
+- Do not allow to rename a format's short name if the format is used by a
+  converter. This prevents a crash (bug 6815).
+
 - Box dialog: only shaded boxes can have multiple paragraphs when there
   is no inner box.
 
@@ -81,6 +84,7 @@ What's new
 - When undo returns to a state where the file was saved, make sure to
   reset the (changed) status (bug 3733).
 
+
 * DOCUMENTATION AND LOCALIZATION