diff --git a/pkgs/development/compilers/gcc/libstdc++-hook.sh b/pkgs/development/compilers/gcc/libstdc++-hook.sh
index 2d30c845b5a3..893bbbc0c2dc 100644
--- a/pkgs/development/compilers/gcc/libstdc++-hook.sh
+++ b/pkgs/development/compilers/gcc/libstdc++-hook.sh
@@ -1,2 +1,2 @@
-export NIX_CXXSTDLIB_COMPILE+="-isystem $(echo -n @gcc@/include/c++/*) -isystem $(echo -n @gcc@/include/c++/*)/$(@gcc@/bin/gcc -dumpmachine)"
+export NIX_CXXSTDLIB_COMPILE+=" -isystem $(echo -n @gcc@/include/c++/*) -isystem $(echo -n @gcc@/include/c++/*)/$(@gcc@/bin/gcc -dumpmachine)"
 export NIX_CXXSTDLIB_LINK=" -stdlib=libstdc++"