diff --git a/Source/Platform.h b/Source/Platform.h
index 791bdb5a..39c7b572 100644
--- a/Source/Platform.h
+++ b/Source/Platform.h
@@ -448,6 +448,7 @@ typedef WORD LANGID;
 #  define WS_EX_RIGHT 0x1000
 #  define WS_EX_RIGHTSCROLLBAR 0
 #  define WS_EX_RTLREADING 0x2000
+#  define WS_EX_LEFTSCROLLBAR 0x4000
 
 #  define TVS_RTLREADING 64