diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 9d3cea7a0..ea1770fc5 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -49,8 +49,7 @@ LocalStore::LocalStore()
     checkStoreNotSymlink();
 
     Path globalLockPath = nixDBPath + "/big-lock";
-    globalLock = open(globalLockPath.c_str(), O_RDWR | O_CREAT, 0666);
-    if (globalLock == -1) throw SysError(format("opening file `%1%'") % globalLockPath);
+    globalLock = openLockFile(globalLockPath.c_str(), true);
     
     if (!lockFile(globalLock, ltRead, false)) {
         printMsg(lvlError, "waiting for the big Nix store lock...");
diff --git a/src/libstore/upgrade-schema.cc b/src/libstore/upgrade-schema.cc
index d54e29bd9..450a7c8d0 100644
--- a/src/libstore/upgrade-schema.cc
+++ b/src/libstore/upgrade-schema.cc
@@ -22,6 +22,11 @@ void LocalStore::upgradeStore12()
 {
 #if OLD_DB_COMPAT
     
+#ifdef __CYGWIN__
+    /* Cygwin can't upgrade a read lock to a write lock... */
+    lockFile(globalLock, ltNone, true);
+#endif
+
     if (!lockFile(globalLock, ltWrite, false)) {
         printMsg(lvlError, "waiting for exclusive access to the Nix store...");
         lockFile(globalLock, ltWrite, true);