diff --git a/contrib/mdx/CMakeLists.txt b/contrib/mdx/CMakeLists.txt
index 023457e..20d0331 100644
--- a/contrib/mdx/CMakeLists.txt
+++ b/contrib/mdx/CMakeLists.txt
@@ -1,4 +1,4 @@
-if(TARGET Motif::Motif AND TARGET X11::Xt)
+if(TARGET Motif::Motif AND TARGET X11::Xt AND TARGET X11::X11)
     add_executable(mdx
         src/graphx_mdx.c
         src/rdf_reader_subs.f
@@ -12,5 +12,6 @@ if(TARGET Motif::Motif AND TARGET X11::Xt)
     target_link_libraries(mdx PUBLIC
         Motif::Motif
         X11::Xt
+        X11::X11
         )
 endif()