diff --git a/var/spack/repos/builtin/packages/mumps/package.py b/var/spack/repos/builtin/packages/mumps/package.py
index a56bc111e2..de34b6aa19 100644
--- a/var/spack/repos/builtin/packages/mumps/package.py
+++ b/var/spack/repos/builtin/packages/mumps/package.py
@@ -241,7 +241,7 @@ def write_makefile_inc(self):
         else:
             makefile_conf.extend([
                 'LIBEXT  = .a',
-                'AR = ar vr',
+                'AR = ar vr ',
                 'RANLIB = ranlib'
             ])