diff --git a/lib/spack/spack/compilers/msvc.py b/lib/spack/spack/compilers/msvc.py
index d7576b78e6a..86d51461aa4 100644
--- a/lib/spack/spack/compilers/msvc.py
+++ b/lib/spack/spack/compilers/msvc.py
@@ -160,6 +160,8 @@ def setup_custom_environment(self, pkg, env):
     def fc_version(cls, fc):
         # We're using intel for the Fortran compilers, which exist if
         # ONEAPI_ROOT is a meaningful variable
+        if not sys.platform == "win32":
+            return "unknown"
         fc_ver = cls.default_version(fc)
         avail_fc_version.add(fc_ver)
         fc_path[fc_ver] = fc