diff --git a/samba.spec b/samba.spec
index 6bfb75c..b8ffdac 100644
--- a/samba.spec
+++ b/samba.spec
@@ -194,8 +194,8 @@
 %global _systemd_extra "Environment=KRB5CCNAME=FILE:/run/samba/krb5cc_samba"
 
 # Make a copy of this variable to prevent repeated evaluation of the
-# embedded shell command.
-%global python3_sitearch %{python3_sitearch}
+# embedded shell command.  Avoid recursive macro definition if undefined.
+%{?python3_sitearch: %global python3_sitearch %{python3_sitearch}}
 
 Name:           samba
 Version:        %{samba_version}