diff --git a/lib/spack/spack/build_systems/python.py b/lib/spack/spack/build_systems/python.py
index a308e77cb93..2d003f38e3e 100644
--- a/lib/spack/spack/build_systems/python.py
+++ b/lib/spack/spack/build_systems/python.py
@@ -4,6 +4,7 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 import inspect
 import os
+import re
 import shutil
 
 import llnl.util.tty as tty
@@ -144,6 +145,8 @@ def import_modules(self):
             modules.append(path.replace(root + os.sep, '', 1).replace(
                 '.py', '').replace('/', '.'))
 
+        modules = [mod for mod in modules if re.match('[a-zA-Z0-9._]+$', mod)]
+
         tty.debug('Detected the following modules: {0}'.format(modules))
 
         return modules
diff --git a/lib/spack/spack/build_systems/sip.py b/lib/spack/spack/build_systems/sip.py
index 814aa2605b7..49fdd621ee1 100644
--- a/lib/spack/spack/build_systems/sip.py
+++ b/lib/spack/spack/build_systems/sip.py
@@ -5,6 +5,7 @@
 
 import inspect
 import os
+import re
 
 import llnl.util.tty as tty
 from llnl.util.filesystem import find, join_path, working_dir
@@ -81,6 +82,8 @@ def import_modules(self):
             modules.append(path.replace(root + os.sep, '', 1).replace(
                 '.py', '').replace('/', '.'))
 
+        modules = [mod for mod in modules if re.match('[a-zA-Z0-9._]+$', mod)]
+
         tty.debug('Detected the following modules: {0}'.format(modules))
 
         return modules