diff --git a/guix/build/activation.scm b/guix/build/activation.scm
index 62e69a9152..bc62a94e01 100644
--- a/guix/build/activation.scm
+++ b/guix/build/activation.scm
@@ -126,7 +126,8 @@ (define activate-user
   ;; Then create the groups.
   (for-each (match-lambda
              ((name password gid)
-              (add-group name #:gid gid #:password password)))
+              (unless (false-if-exception (getgrnam name))
+                (add-group name #:gid gid #:password password))))
             groups)
 
   ;; Finally create the other user accounts.