diff --git a/xs/Build.PL b/xs/Build.PL
index 6ae9ad9b6..23b10273d 100644
--- a/xs/Build.PL
+++ b/xs/Build.PL
@@ -20,7 +20,7 @@ $ENV{LD_RUN_PATH} //= "";
 # NOGDI            : prevents inclusion of wingdi.h which defines functions Polygon() and Polyline() in global namespace
 # BOOST_ASIO_DISABLE_KQUEUE : prevents a Boost ASIO bug on OS X: https://svn.boost.org/trac/boost/ticket/5339
 my @cflags = qw(-D_GLIBCXX_USE_C99 -DHAS_BOOL -DNOGDI -DSLIC3RXS -DBOOST_ASIO_DISABLE_KQUEUE -Dexprtk_disable_rtl_io_file -Dexprtk_disable_return_statement -Dexprtk_disable_rtl_vecops -Dexprtk_disable_string_capabilities -Dexprtk_disable_enhanced_features);
-push @cflags, "-DSLIC3R_BUILD_COMMIT=$ENV{SLIC3R_GIT_VERSION}";
+push @cflags, "-DSLIC3R_BUILD_COMMIT=$ENV{SLIC3R_GIT_VERSION}" if defined $ENV{SLIC3R_GIT_VERSION};
 
 if ($cpp_guess->is_gcc)	{
 	# GCC is pedantic with c++11 std, so undefine strict ansi to get M_PI back