diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index d768d4429..1fc5d4181 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1895,7 +1895,7 @@ void DerivationGoal::startBuilder()
            build user. */
         Path chrootStoreDir = chrootRootDir + settings.nixStore;
         createDirs(chrootStoreDir);
-        chmod_(chrootStoreDir, 0735);
+        chmod_(chrootStoreDir, 01775);
 
         if (chown(chrootStoreDir.c_str(), 0, buildUser.getGID()) == -1)
             throw SysError(format("cannot change ownership of ‘%1%’") % chrootStoreDir);
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 3ec467649..91149b30f 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -256,7 +256,7 @@ LocalStore::LocalStore(bool reserveSpace)
         if (chmod(perUserDir.c_str(), 01777) == -1)
             throw SysError(format("could not set permissions on ‘%1%’ to 1777") % perUserDir);
 
-        mode_t perm = 01735;
+        mode_t perm = 01775;
 
         struct group * gr = getgrnam(settings.buildUsersGroup.c_str());
         if (!gr)