diff --git a/src/libstore/unix/build/local-derivation-goal.cc b/src/libstore/unix/build/local-derivation-goal.cc
index 0eda8455f..e3e3a4c9b 100644
--- a/src/libstore/unix/build/local-derivation-goal.cc
+++ b/src/libstore/unix/build/local-derivation-goal.cc
@@ -2008,7 +2008,7 @@ void LocalDerivationGoal::runChild()
             if (chdir(chrootRootDir.c_str()) == -1)
                 throw SysError("cannot change directory to '%1%'", chrootRootDir);
 
-            if (mkdir("real-root", 0) == -1)
+            if (mkdir("real-root", 0500) == -1)
                 throw SysError("cannot create real-root directory");
 
             if (pivot_root(".", "real-root") == -1)