diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 1ebe106d3..06fac38b1 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -10,7 +10,7 @@ option(PROFILE "Build with gprof profiling output." OFF)
 option(COVERAGE "Build with gcov code coverage profiling." OFF)
 
 # only on newer GCCs: -ftemplate-backtrace-limit=0
-add_compile_options(-DNO_PERL  -DM_PI=3.14159265358979323846 -D_GLIBCXX_USE_C99 -DHAS_BOOL -DNOGDI -DBOOST_ASIO_DISABLE_KQUEUE)
+add_compile_options(-DNO_PERL -DM_PI=3.14159265358979323846 -DHAS_BOOL -DNOGDI -DBOOST_ASIO_DISABLE_KQUEUE)
 
 if (MSVC)
     add_compile_options(-W3)
diff --git a/xs/Build.PL b/xs/Build.PL
index 63f8308d4..35356b873 100644
--- a/xs/Build.PL
+++ b/xs/Build.PL
@@ -15,11 +15,10 @@ my $linux = $^O eq 'linux';
 # prevent an annoying concatenation warning by Devel::CheckLib
 $ENV{LD_RUN_PATH} //= "";
 
-# _GLIBCXX_USE_C99 : to get the long long type for g++
 # HAS_BOOL         : stops Perl/lib/CORE/handy.h from doing "#  define bool char" for MSVC
 # NOGDI            : prevents inclusion of wingdi.h which defines functions Polygon() and Polyline() in global namespace
 # BOOST_ASIO_DISABLE_KQUEUE : prevents a Boost ASIO bug on OS X: https://svn.boost.org/trac/boost/ticket/5339
-my @cflags = qw(-D_GLIBCXX_USE_C99 -DHAS_BOOL -DNOGDI -DSLIC3RXS -DBOOST_ASIO_DISABLE_KQUEUE -Dexprtk_disable_rtl_io_file -Dexprtk_disable_return_statement -Dexprtk_disable_rtl_vecops -Dexprtk_disable_string_capabilities -Dexprtk_disable_enhanced_features);
+my @cflags = qw(-DHAS_BOOL -DNOGDI -DSLIC3RXS -DBOOST_ASIO_DISABLE_KQUEUE -Dexprtk_disable_rtl_io_file -Dexprtk_disable_return_statement -Dexprtk_disable_rtl_vecops -Dexprtk_disable_string_capabilities -Dexprtk_disable_enhanced_features);
 push @cflags, "-DSLIC3R_BUILD_COMMIT=$ENV{SLIC3R_GIT_VERSION}" if defined $ENV{SLIC3R_GIT_VERSION};
 
 # std=c++11 Enforce usage of C++11 (required now). Minimum compiler supported: gcc 4.9, clang 3.3, MSVC 14.0