diff --git a/bin/spack b/bin/spack
index c62871d6a6750d77ddcd30fdad0857db974db7a7..171ee0f7241e8e5275a655d383461c32206a54ec 100755
--- a/bin/spack
+++ b/bin/spack
@@ -31,6 +31,18 @@ if sys.version_info[:2] == (2, 6):
 
 sys.path.insert(0, spack_external_libs)
 
+# Here we delete ruamel.yaml in case it has been already imported from site
+# (see #9206 for a broader description of the issue).
+#
+# Briefly: ruamel.yaml produces a .pth file when installed with pip that
+# makes the site installed package the preferred one, even tough sys.path
+# is modified to point to another version of ruamel.yaml.
+if 'ruamel.yaml' in sys.modules:
+    del sys.modules['ruamel.yaml']
+
+if 'ruamel' in sys.modules:
+    del sys.modules['ruamel']
+
 # Once we've set up the system path, run the spack main method
 import spack.main  # noqa
 sys.exit(spack.main.main())