Index: sources/pyside2/CMakeLists.txt
--- sources/pyside2/CMakeLists.txt.orig
+++ sources/pyside2/CMakeLists.txt
@@ -239,6 +239,7 @@ set(GENERATOR_EXTRA_FLAGS --generator-set=shiboken
                           --enable-parent-ctor-heuristic
                           --enable-pyside-extensions
                           --enable-return-value-heuristic
+                          -I/usr/X11R6/include
                           --use-isnull-as-nb_nonzero)
 use_protected_as_public_hack()
 
