diff --git a/Makefile b/Makefile
index c3bd372..e1d6f96 100644
--- a/Makefile
+++ b/Makefile
@@ -7,7 +7,7 @@ include ./etc/make/emacs.mk
 include ./etc/config/$(CONFIG).mk
 include ./bench/config.mk
 
-$(info using configuration CONFIG=$(CONFIG))
+$(info ==ATRIP== using configuration CONFIG=$(CONFIG))
 
 MAIN = README.org
 OBJ_FILES = $(patsubst %.cxx,%.o,$(filter-out %.hpp,$(SOURCES)))
diff --git a/README.org b/README.org
index 42d4743..53e553e 100644
--- a/README.org
+++ b/README.org
@@ -1283,7 +1283,7 @@ namespace atrip {
       const int rank = Atrip::rank
               , Nv = sliceLength[0]
               , No = sliceLength[1]
-              , a = rankMap.find({rank, it});
+              , a = rankMap.find({static_cast<size_t>(rank), it});
               ;
 
 
@@ -1321,7 +1321,7 @@ namespace atrip {
 
       const int rank = Atrip::rank
               , No = sliceLength[0]
-              , a = rankMap.find({rank, it})
+              , a = rankMap.find({static_cast<size_t>(rank), it})
               ;
 
       sliceIntoVector( sources[it]
@@ -1358,7 +1358,7 @@ namespace atrip {
       const int Nv = sliceLength[0]
               , No = sliceLength[1]
               , rank = Atrip::rank
-              , el = rankMap.find({rank, it})
+              , el = rankMap.find({static_cast<size_t>(rank), it})
               , a = el % Nv
               , b = el / Nv
               ;
@@ -1397,7 +1397,7 @@ namespace atrip {
       const int Nv = from.lens[0]
               , No = sliceLength[1]
               , rank = Atrip::rank
-              , el = rankMap.find({rank, it})
+              , el = rankMap.find({static_cast<size_t>(rank), it})
               , a = el % Nv
               , b = el / Nv
               ;
@@ -1438,7 +1438,7 @@ namespace atrip {
       const int Nv = from.lens[0]
               , No = sliceLength[1]
               , rank = Atrip::rank
-              , el = rankMap.find({rank, it})
+              , el = rankMap.find({static_cast<size_t>(rank), it})
               , a = el % Nv
               , b = el / Nv
               ;
diff --git a/etc/config/clang.mk b/etc/config/clang.mk
new file mode 100644
index 0000000..b859087
--- /dev/null
+++ b/etc/config/clang.mk
@@ -0,0 +1,4 @@
+include ./etc/config/gcc.mk
+
+export OMPI_CC=clang
+export OMPI_CXX=clang++
diff --git a/etc/config/gcc.mk b/etc/config/gcc.mk
index d57e353..b02039b 100644
--- a/etc/config/gcc.mk
+++ b/etc/config/gcc.mk
@@ -8,6 +8,8 @@ CXXFLAGS += -I$(ATRIP_ROOT)/include
 
 CXXFLAGS += -I$(CTF_INCLUDE_PATH)
 CXXFLAGS += -fPIC
+CXXFLAGS += -std=c++11
+CXXFLAGS += -pedantic -Wall
 
 LDFLAGS += -fopenmp
 LDFLAGS += -Wl,-Bstatic
diff --git a/etc/make/ctf_vars.mk b/etc/make/ctf_vars.mk
index 1de08fa..3c351c0 100644
--- a/etc/make/ctf_vars.mk
+++ b/etc/make/ctf_vars.mk
@@ -2,7 +2,7 @@ CTF_REPOSITORY = https://github.com/cyclops-community/ctf
 CTF_COMMIT    ?= v1.5.0
 
 CTF_SRC_PATH     = $(ATRIP_ROOT)/extern/src/ctf/$(CTF_COMMIT)
-CTF_BUILD_PATH   = $(ATRIP_ROOT)/extern/build/ctf/$(CTF_COMMIT)
+CTF_BUILD_PATH   = $(ATRIP_ROOT)/extern/build/$(CONFIG)/ctf/$(CTF_COMMIT)
 
 CTF_CONFIG_FLAGS =
 
diff --git a/shell.nix b/shell.nix
index d2c7c13..39b6723 100644
--- a/shell.nix
+++ b/shell.nix
@@ -4,6 +4,9 @@ pkgs.mkShell rec {
 
   buildInputs = with pkgs; [
 
+    clang
+    llvmPackages.openmp
+
     coreutils
     git
 
@@ -19,9 +22,7 @@ pkgs.mkShell rec {
   openblas =  pkgs.openblas.override {
     enableStatic = true;
   };
-  */
 
-  /*
   scalapack = import ./etc/nix/scalapack.nix {
     lib = pkgs.lib;
     stdenv = pkgs.stdenv;