Invalid code generated from UI files when building linguist tool

FAILED: qttools/src/linguist/linguist/CMakeFiles/linguist.dir/phraseview.cpp.o  
/usr/bin/clang++ -DQFORMINTERNAL_NAMESPACE -DQT_CORE_LIB -DQT_GUI_LIB -DQT_KEYWORDS -DQT_NO_CAST_FROM_ASCII -DQT_NO_CAST_TO_ASCII -DQT_NO_DEBUG -DQT_NO_EXCEPTIONS -DQT_NO_JAVA_STYLE_ITERATORS -DQT_NO_NARROWING_C
ONVERSIONS_IN_CONNECT -DQT_OPENGLWIDGETS_LIB -DQT_OPENGL_LIB -DQT_PRINTSUPPORT_LIB -DQT_STRICT_QLIST_ITERATORS -DQT_UITOOLS_LIB -DQT_WIDGETS_LIB -D_LARGEFILE64_SOURCE -D_LARGEFILE_SOURCE -I/home/nico/workspace/q
t6/qttools/src/linguist/linguist/linguist_autogen/include -I/home/nico/workspace/qt6/qttools/src/linguist/linguist -I/home/nico/workspace/qt6/qttools/src/linguist/linguist/../shared -I/home/nico/workspace/qt6/qt
base/include -I/home/nico/workspace/qt6/qtbase/include/QtCore -I/home/nico/workspace/qt6/qtbase/mkspecs/linux-clang -I/home/nico/workspace/qt6/qtbase/src/corelib -I/home/nico/workspace/qt6/qtbase/include/QtCore/
6.4.0 -I/home/nico/workspace/qt6/qtbase/include/QtCore/6.4.0/QtCore -I/home/nico/workspace/qt6/qtbase/include/QtGui -I/home/nico/workspace/qt6/qtbase/src/gui -I/home/nico/workspace/qt6/qtbase/include/QtGui/6.4.0
 -I/home/nico/workspace/qt6/qtbase/include/QtGui/6.4.0/QtGui -I/home/nico/workspace/qt6/qtbase/include/QtPrintSupport -I/home/nico/workspace/qt6/qtbase/include/QtWidgets -I/home/nico/workspace/qt6/qttools/src/ui
tools -I/home/nico/workspace/qt6/qtbase/include/QtUiTools/6.4.0 -I/home/nico/workspace/qt6/qtbase/include/QtUiTools/6.4.0/QtUiTools -I/home/nico/workspace/qt6/qtbase/include/QtUiTools -I/home/nico/workspace/qt6/
qtbase/include/QtOpenGLWidgets -I/home/nico/workspace/qt6/qtbase/include/QtOpenGL -g -DNDEBUG -O2 -fPIE -fvisibility=hidden -fvisibility-inlines-hidden -Wall -Wextra -fno-exceptions -fPIC -Werror "-Wno-error=#wa
rnings" -Wno-error=deprecated-declarations -Wno-error=deprecated-enum-enum-conversion -std=c++17 -MD -MT qttools/src/linguist/linguist/CMakeFiles/linguist.dir/phraseview.cpp.o -MF qttools/src/linguist/linguist/C
MakeFiles/linguist.dir/phraseview.cpp.o.d -o qttools/src/linguist/linguist/CMakeFiles/linguist.dir/phraseview.cpp.o -c /home/nico/workspace/qt6/qttools/src/linguist/linguist/phraseview.cpp

In file included from /home/nico/workspace/qt6/qttools/src/linguist/linguist/phraseview.cpp:30:

In file included from /home/nico/workspace/qt6/qttools/src/linguist/linguist/mainwindow.h:33:

/home/nico/workspace/qt6/qttools/src/linguist/linguist/linguist_autogen/include/ui_mainwindow.h:3:15: error: unknown type name 'C'

** Copyright (C) 2016 The Qt Company Ltd.

              ^

/home/nico/workspace/qt6/qttools/src/linguist/linguist/linguist_autogen/include/ui_mainwindow.h:3:18: error: expected function body after function declarator

** Copyright (C) 2016 The Qt Company Ltd.

                 ^

In file included from /home/nico/workspace/qt6/qttools/src/linguist/linguist/phraseview.cpp:30:

In file included from /home/nico/workspace/qt6/qttools/src/linguist/linguist/mainwindow.h:36:

In file included from /home/nico/workspace/qt6/qttools/src/linguist/linguist/finddialog.h:32:

/home/nico/workspace/qt6/qttools/src/linguist/linguist/linguist_autogen/include/ui_finddialog.h:3:15: error: unknown type name 'C'

** Copyright (C) 2016 The Qt Company Ltd.

              ^

/home/nico/workspace/qt6/qttools/src/linguist/linguist/linguist_autogen/include/ui_finddialog.h:3:18: error: expected function body after function declarator

** Copyright (C) 2016 The Qt Company Ltd.

                 ^

4 errors generated.

*********************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**