diff --git a/libreoffice.spec b/libreoffice.spec
index 3ff4d7d..0017c72 100644
--- a/libreoffice.spec
+++ b/libreoffice.spec
@@ -49,7 +49,7 @@ Summary:	Office suite
 Name:		libreoffice
 Epoch:		1
 Version:	6.3.5
-Release:	5
+Release:	6
 License:	(MPLv1.1 or LGPLv3+) and LGPLv3 and LGPLv2+ and BSD and (MPLv1.1 or GPLv2 or LGPLv2 or Netscape) and Public Domain and ASL 2.0 and Artistic
 Group:		Office
 Url:		http://www.libreoffice.org
@@ -2962,9 +2962,15 @@ export CCACHE_DIR=%{ccachedir}
 %endif
 
 %if %{with clang}
-%global optflags $(echo %{optflags} | sed -e 's/-fvar-tracking-assignments//g' -e 's/-frecord-gcc-switches//g' -e 's/-ffat-lto-objects//g')
-%global optflags %{optflags} -stdlib=libc++ -nostdinc++ -I/usr/include/c++/v1
-%global ldflags %{ldflags} -stdlib=libc++ -nostdinc++ -lc++ -lc++abi
+%setup_compile_flags
+# libstdc++ from gcc5 is too old, use LLVM libc++
+# https://libcxx.llvm.org/docs/UsingLibcxx.html
+# clang -c -stdlib=libc++ ->
+# -> "argument unused during compilation: '-stdlib=libc++'" ->
+# -> -Wno-unused-command-line-argument
+export CXXFLAGS="$CXXFLAGS -stdlib=libc++ -nostdinc++ -I/usr/include/c++/v1 -Wno-unused-command-line-argument"
+# Try to avoid overlinkg C code with libc++ by adjusting CXXFLAGS instead of LDFLAGS
+export CXXFLAGS="$CXXFLAGS -Xlinker -lc++ -Xlinker -lc++abi"
 %clang_gcc_wrapper
 export CPP=""
 %else