diff --git a/.gitignore b/.gitignore
index 649440de93..f65ad52175 100644
--- a/.gitignore
+++ b/.gitignore
@@ -24,3 +24,5 @@ src/lyx_commit_hash.h
 src/moc_PreviewLoader.cpp
 src/support/moc_ConsoleApplicationPrivate.cpp
 src/support/moc_FileMonitor.cpp
+3rdparty/mythes/liblyxmythes.a
+
diff --git a/lib/symbols b/lib/symbols
index 8927d5211c..14247cfc4f 100644
--- a/lib/symbols
+++ b/lib/symbols
@@ -1134,6 +1134,7 @@ pod                lyxblacktext  0   0 func     x     amsmath
 # mathtools.sty
 vcentcolon         cmr          58  58    mathrel :             mathtools
 ordinarycolon      cmr          58  58    mathrel :             mathtools
+\def\bigtimes{\mathop{\diagup\kern-16mu\diagdown}}              mathtools
 \def\dblcolon{\vcentcolon\mathrel{\kern-0.9mu}\vcentcolon}      mathrel ::       mathtools
 \def\coloneqq{\vcentcolon\mathrel{\kern-1.2mu}=}                mathrel ≔ mathtools
 \def\Coloneqq{\dblcolon\mathrel{\kern-1.2mu}=}                  mathrel ::=      mathtools