Index: setupext.py
--- setupext.py.orig
+++ setupext.py
@@ -443,6 +443,7 @@ class Matplotlib(SetupPackage):
         ext = Extension(
             "matplotlib._qhull", ["src/_qhull_wrapper.cpp"],
             define_macros=[("MPL_DEVNULL", os.devnull)])
+        ext.include_dirs.extend(['${PREFIX}/include'])
         add_numpy_flags(ext)
         Qhull.add_flags(ext)
         yield ext
@@ -456,6 +457,7 @@ class Matplotlib(SetupPackage):
             libraries={"linux": ["dl"], "win32": ["comctl32", "psapi"],
                        "cygwin": ["comctl32", "psapi"]}.get(sys.platform, []),
             extra_link_args={"win32": ["-mwindows"]}.get(sys.platform, []))
+        ext.include_dirs.extend(['${X11BASE}/include'])
         add_numpy_flags(ext)
         add_libagg_flags(ext)
         yield ext