diff --git a/vtk.spec b/vtk.spec
index 3e50123..27fd3b6 100644
--- a/vtk.spec
+++ b/vtk.spec
@@ -209,6 +209,8 @@ Requires: PEGTL-devel%{?_isa}
 Requires: proj-devel%{?_isa}
 Requires: pugixml-devel%{?_isa}
 Requires: sqlite-devel%{?_isa}
+Requires: libX11-devel%{?_isa}
+Requires: libXext-devel%{?_isa}
 Requires: libXt-devel%{?_isa}
 Requires: mysql-devel%{?_isa}
 Requires: netcdf-cxx-devel%{?_isa}