diff --git a/Makefile.am b/Makefile.am
index 6386176..1e81ff2 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -2,6 +2,16 @@ include ./etc/make/emacs.mk
 
 SUBDIRS = src bench
 
+if WITH_BUILD_CTF
+CTF_COMMIT         = 968f8f9eb6aab1d6b67d2fcc1a70c9fc3b98adfa
+CTF_GIT_REPOSITORY = https://github.com/cc4s/ctf
+CTF_BUILD_PATH     = $(builddir)/extern/build/$(CONFIG)/ctf/$(CTF_COMMIT)
+CTF_SRC_PATH       = $(builddir)/extern/src/$(CONFIG)/ctf/$(CTF_COMMIT)
+include $(srcdir)/etc/make/ctf.mk
+src: ctf
+SUBDIRS += extern/ctf/
+endif
+
 _ATRIPSRCS = Sources.mk
 ## include $(_ATRIPSRCS)
 
diff --git a/configure.ac b/configure.ac
index 315e522..a8e962c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -30,6 +30,15 @@ AC_ARG_WITH(libctf-prefix,
                            LIBCTF_LD_LIBRARY_PATH="`readlink -f $withval`/lib";
                            BUILD_CTF=NO],
             [BUILD_CTF=YES])
+AM_CONDITIONAL([WITH_BUILD_CTF], [test x${BUILD_CTF} = xYES])
+
+AC_ARG_WITH([clang-check],
+            [AS_HELP_STRING([--with-clang-check],
+                            [Check with clang-check])],
+            [clang_check=YES;
+             AC_CHECK_PROG([CLANG_CHECK], [clang-check])],
+            [clang_check=NO])
+AM_CONDITIONAL([WITH_CLANG_CHECK], [test x${clang_check} = xYES])
 
 AC_ARG_WITH(dgemm,
             AS_HELP_STRING([--without-dgemm], [Disable dgemm]),
@@ -77,7 +86,7 @@ CXX=${MPICXX}
 
 dnl ---------- CHECK CTF
 if test xYES = x${BUILD_CTF}; then
-  AC_MSG_ERROR([Sorry, building CTF not supported yet provide a build path
+  AC_MSG_WARN([Sorry, building CTF not supported yet provide a build path
                       with --with-libctf-prefix=path])
 else
   CPPFLAGS="$CPPFLAGS -I${LIBCTF_CPATH}"
diff --git a/etc/make/ctf.mk b/etc/make/ctf.mk
index a75ee2d..f4d43e5 100644
--- a/etc/make/ctf.mk
+++ b/etc/make/ctf.mk
@@ -10,7 +10,7 @@ $(CTF_SRC_PATH)/configure:
 
 $(CTF_BUILD_PATH)/Makefile: $(CTF_SRC_PATH)/configure
 	mkdir -p $(CTF_BUILD_PATH)
-	cd $(CTF_BUILD_PATH) && $(CTF_SRC_PATH)/configure $(CTF_CONFIG_FLAGS)
+	cd $(CTF_BUILD_PATH) && $(abspath $(CTF_SRC_PATH))/configure $(CTF_CONFIG_FLAGS)
 
 $(CTF_STATIC_LIB): $(CTF_BUILD_PATH)/Makefile
 	$(info Compiling $@)
@@ -21,8 +21,3 @@ ctf: $(CTF_STATIC_LIB)
 
 ctf-clean:
 	rm -rf $(CTF_BUILD_PATH)
-
-EXTERNAL_DEPENDENCIES += ctf
-STATIC_LIBS += $(CTF_LDFLAGS)
-INCLUDE_FLAGS += $(CTF_INCLUDE)
-REQUIRED_MAKEVARS += CTF_COMMIT CTF_BUILD_PATH CTF_GIT_REPOSITORY CTF_SRC_PATH
diff --git a/etc/nix/clang.nix b/etc/nix/clang.nix
index 89afa25..3c14a15 100644
--- a/etc/nix/clang.nix
+++ b/etc/nix/clang.nix
@@ -7,6 +7,8 @@
   ];
 
   shellHook = ''
+    export CC=clang
+    export CXX=clang++
     export OMPI_CC=clang
     export OMPI_CXX=clang++
   '';