diff --git a/guix/build/install.scm b/guix/build/install.scm
index d0019300ff..5bafe905de 100644
--- a/guix/build/install.scm
+++ b/guix/build/install.scm
@@ -75,7 +75,7 @@ (define (directives store)
 STORE."
   `(;; Note: the store's GID is fixed precisely so we can set it here rather
     ;; than at activation time.
-    (directory ,store 0 30000)
+    (directory ,store 0 30000 #o1775)
 
     (directory "/etc")
     (directory "/var/log")                          ; for dmd