diff --git a/var/spack/repos/builtin/packages/triangle/package.py b/var/spack/repos/builtin/packages/triangle/package.py
index 882b8b472b3..f8703f33b31 100644
--- a/var/spack/repos/builtin/packages/triangle/package.py
+++ b/var/spack/repos/builtin/packages/triangle/package.py
@@ -18,6 +18,8 @@ class Triangle(Package):
 
     version('1.6', sha256='1766327add038495fa3499e9b7cc642179229750f7201b94f8e1b7bee76f8480')
 
+    depends_on('libx11', type='link')
+
     def install(self, spec, prefix):
         make()
         mkdirp(prefix.bin)