diff --git a/Documentation/input/multi-touch-protocol.txt b/Documentation/input/multi-touch-protocol.txt
index 2c17961..de139b1 100644
--- a/Documentation/input/multi-touch-protocol.txt
+++ b/Documentation/input/multi-touch-protocol.txt
@@ -80,6 +80,8 @@
 by noting that the largest supported BTN_TOOL_*TAP event is larger than the
 total number of type B slots reported in the absinfo for the ABS_MT_SLOT axis.
 
+The minimum value of the ABS_MT_SLOT axis must be 0.
+
 Protocol Example A
 ------------------