diff --git a/var/spack/repos/builtin/packages/mpich/package.py b/var/spack/repos/builtin/packages/mpich/package.py
index 8965c3d711..44c94a6d8f 100644
--- a/var/spack/repos/builtin/packages/mpich/package.py
+++ b/var/spack/repos/builtin/packages/mpich/package.py
@@ -187,6 +187,9 @@ class Mpich(AutotoolsPackage):
     conflicts('+pci', when='@:3.2~hydra')
     conflicts('+libxml2', when='@:3.2~hydra')
 
+    # see https://github.com/pmodels/mpich/pull/5031
+    conflicts('%clang@:7', when='@3.4:')
+
     @classmethod
     def determine_version(cls, exe):
         output = Executable(exe)(output=str, error=str)