diff --git a/var/spack/repos/builtin/packages/boost/package.py b/var/spack/repos/builtin/packages/boost/package.py
index a57b2e5bac..3fd01f2384 100644
--- a/var/spack/repos/builtin/packages/boost/package.py
+++ b/var/spack/repos/builtin/packages/boost/package.py
@@ -44,10 +44,6 @@ class Boost(Package):
     version("1.66.0", sha256="5721818253e6a0989583192f96782c4a98eb6204965316df9f5ad75819225ca9")
     version("1.65.1", sha256="9807a5d16566c57fd74fb522764e0b134a8bbe6b6e8967b83afefd30dcd3be81")
     version("1.65.0", sha256="ea26712742e2fb079c2a566a31f3266973b76e38222b9f88b387e3c8b2f9902c")
-    # NOTE: 1.64.0 seems fine for *most* applications, but if you need
-    #       +python and +mpi, there seem to be errors with out-of-date
-    #       API calls from mpi/python.
-    #       See: https://github.com/spack/spack/issues/3963
     version("1.64.0", sha256="7bcc5caace97baa948931d712ea5f37038dbb1c5d89b43ad4def4ed7cb683332")
     version("1.63.0", sha256="beae2529f759f6b3bf3f4969a19c2e9d6f0c503edcb2de4a61d1428519fcb3b0")
     version("1.62.0", sha256="36c96b0f6155c98404091d8ceb48319a28279ca0333fba1ad8611eb90afb2ca0")
@@ -245,6 +241,13 @@ def libs(self):
     conflicts("cxxstd=98", when="+fiber")  # Fiber requires >=C++11.
     conflicts("~context", when="+fiber")  # Fiber requires Context.
 
+    # NOTE: 1.64.0 seems fine for *most* applications, but if you need
+    #       +python and +mpi, there seem to be errors with out-of-date
+    #       API calls from mpi/python.
+    #       See: https://github.com/spack/spack/issues/3963
+    conflicts("@1.64.0", when="+python", msg="Errors with out-of-date API calls from Python")
+    conflicts("@1.64.0", when="+mpi", msg="Errors with out-of-date API calls from MPI")
+
     conflicts("+taggedlayout", when="+versionedlayout")
     conflicts("+numpy", when="~python")