diff --git a/packages/x11/lib/libX11/package.mk b/packages/x11/lib/libX11/package.mk
index e81525ced5..db2c6c8272 100644
--- a/packages/x11/lib/libX11/package.mk
+++ b/packages/x11/lib/libX11/package.mk
@@ -56,4 +56,5 @@ pre_configure_target() {
   export CPPFLAGS_FOR_BUILD="$HOST_CPPFLAGS"
   export CFLAGS_FOR_BUILD="$HOST_CFLAGS"
   export LDFLAGS_FOR_BUILD="$HOST_LDFLAGS"
+  unset PKG_CONFIG_ALLOW_SYSTEM_CFLAGS
 }