diff --git a/SPECS/gcc.spec b/SPECS/gcc.spec
index 70dd6e7d..4fd1342c 100644
--- a/SPECS/gcc.spec
+++ b/SPECS/gcc.spec
@@ -46,7 +46,7 @@
 %else
 %global build_libitm 0
 %endif
-%global build_cloog 0
+%global build_cloog 1
 %global build_libstdcxx_docs 0
 %ifarch %{ix86} x86_64 ppc ppc64 ppc64le ppc64p7 s390 s390x %{arm} aarch64
 %global attr_ifunc 1
@@ -1243,10 +1243,13 @@ ISL_FLAG_PIC=-fPIC
 %else
 ISL_FLAG_PIC=-fpic
 %endif
+%ifarch x86_64
+CLOOG_OPT_FLAGS="-m64 -O3 -march=core2 -mtune=core2 -mmmx -msse -msse2 -mssse3 -msse4 -msse4.1 -msse4.2 -mavx"
+%endif
 cd isl-build
 ../../isl-%{isl_version}/configure --disable-shared \
   CC=/usr/bin/gcc CXX=/usr/bin/g++ \
-  CFLAGS="${CFLAGS:-%optflags} $ISL_FLAG_PIC" --prefix=`cd ..; pwd`/isl-install
+  CFLAGS="${CLOOG_OPT_FLAGS} $ISL_FLAG_PIC" --prefix=`cd ..; pwd`/isl-install
 make %{?_smp_mflags}
 make install
 cd ..
@@ -1264,7 +1267,7 @@ isl_prefix=`cd ../isl-install; pwd` \
 ../../cloog-%{cloog_version}/configure --with-isl=system \
   --with-isl-prefix=`cd ../isl-install; pwd` \
   CC=/usr/bin/gcc CXX=/usr/bin/g++ \
-  CFLAGS="${CFLAGS:-%optflags}" CXXFLAGS="${CXXFLAGS:-%optflags}" \
+  CFLAGS="${CLOOG_OPT_FLAGS}" CXXFLAGS="${CLOOG_OPT_FLAGS}" \
    --prefix=`cd ..; pwd`/cloog-install
 sed -i 's|^hardcode_libdir_flag_spec=.*|hardcode_libdir_flag_spec=""|g' libtool
 sed -i 's|^runpath_var=LD_RUN_PATH|runpath_var=DIE_RPATH_DIE|g' libtool