diff --git a/src/libstore/pathlocks.cc b/src/libstore/pathlocks.cc
index d8290815c..645f4cd67 100644
--- a/src/libstore/pathlocks.cc
+++ b/src/libstore/pathlocks.cc
@@ -16,7 +16,7 @@ int openLockFile(const Path & path, bool create)
 {
     AutoCloseFD fd;
 
-    fd = open(path.c_str(), O_RDWR | (create ? O_CREAT : 0), 0666);
+    fd = open(path.c_str(), O_RDWR | (create ? O_CREAT : 0), 0600);
     if (fd == -1 && (create || errno != ENOENT))
         throw SysError(format("opening lock file `%1%'") % path);