MTP2 IAC: Ignore FISU/MSU during proving state of IAC
diff --git a/src/mtp2_iac.erl b/src/mtp2_iac.erl
index 1b756b7..3bb9762 100644
--- a/src/mtp2_iac.erl
+++ b/src/mtp2_iac.erl
@@ -298,6 +298,10 @@
 			send_to_lsc(alignment_complete, LoopDat),
 			fig9_4(LoopDat)
 	end;
+proving(fisu_msu_received, LoopDat) ->
+	% ignore FISU/MSU in this state, as some implementations
+	% (notably yate) seem to send it in violation of the spec
+	{next_state, proving, LoopDat};
 proving(abort_proving, LoopDat) ->
 	% Cp := Cp + 1
 	Cp = LoopDat#iac_state.cp,