include: pstore.idl should import wtypes.idl.
diff --git a/include/pstore.idl b/include/pstore.idl
index 590b905..4f9623e 100644
--- a/include/pstore.idl
+++ b/include/pstore.idl
@@ -16,6 +16,7 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
  */
 
+import "wtypes.idl";
 import "oaidl.idl";
 
 cpp_quote("#define PST_KEY_CURRENT_USER    0")