diff --git a/lib/spack/spack/mixins.py b/lib/spack/spack/mixins.py
index 189c3947ef..ef1d2b7916 100644
--- a/lib/spack/spack/mixins.py
+++ b/lib/spack/spack/mixins.py
@@ -93,7 +93,7 @@ def _filter_compiler_wrappers_impl(pkg_or_builder):
         replacements = []
 
         for idx, (env_var, compiler_path) in enumerate(compiler_vars):
-            if env_var in os.environ:
+            if env_var in os.environ and compiler_path is not None:
                 # filter spack wrapper and links to spack wrapper in case
                 # build system runs realpath
                 wrapper = os.environ[env_var]