diff --git a/depends/config.site.in b/depends/config.site.in
index 4012f5a8d..1df04eec3 100644
--- a/depends/config.site.in
+++ b/depends/config.site.in
@@ -52,7 +52,7 @@ export PATH=$prefix/native/bin:$PATH
 export PKG_CONFIG="`which pkg-config` --static"
 export PKG_CONFIG_LIBDIR=$prefix/lib/pkgconfig
 export PKG_CONFIG_PATH=$prefix/share/pkgconfig
-export CPPFLAGS=-I$prefix/include/
+export CPPFLAGS="-I$prefix/include/ $CPPFLAGS"
 
 export CC="@CC@"
 export CXX="@CXX@"