diff --git a/include/coreinit/messagequeue.h b/include/coreinit/messagequeue.h
index 9bab844..8865525 100644
--- a/include/coreinit/messagequeue.h
+++ b/include/coreinit/messagequeue.h
@@ -22,6 +22,21 @@ typedef enum OSMessageFlags
    OS_MESSAGE_FLAGS_HIGH_PRIORITY   = 1 << 1,
 } OSMessageFlags;
 
+typedef enum OSFunctionType
+{
+  OS_FUNCTION_TYPE_HIO_OPEN                     = 1,
+  OS_FUNCTION_TYPE_HIO_READ_ASYNC               = 2,
+  OS_FUNCTION_TYPE_HIO_WRITE_ASYNC              = 3,
+  OS_FUNCTION_TYPE_FSA_CMD_ASYNC                = 4,
+  OS_FUNCTION_TYPE_FSA_PR_CMD_ASYNC             = 5,
+  OS_FUNCTION_TYPE_FSA_PR_CMD_ASYNC_NO_ALLOC    = 6,
+  OS_FUNCTION_TYPE_FSA_ATTACH_EVENT             = 7,
+  OS_FUNCTION_TYPE_FS_CMD_ASYNC                 = 8,
+  OS_FUNCTION_TYPE_FS_CMD_HANDLER               = 9,
+  OS_FUNCTION_TYPE_FS_ATTACH_EVENT              = 10,
+  OS_FUNCTION_TYPE_FS_STATE_CHANGE_EVENT        = 11,
+} OSFunctionType;
+
 struct OSMessage
 {
    void *message;