From 88db238c509fc6ed70b7ae9b4b6da7f1e2e7f467 Mon Sep 17 00:00:00 2001
From: Esko Dijk <EskoDijk@users.noreply.github.com>
Date: Thu, 26 Feb 2026 04:33:22 +0100
Subject: [PATCH] [coap] clear M flag in Block2 request as required by RFC 7959
 (#12563)

Closes #12560
---
 src/core/coap/coap.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/core/coap/coap.cpp b/src/core/coap/coap.cpp
index 2445b47e0..690fb8d9c 100644
--- a/src/core/coap/coap.cpp
+++ b/src/core/coap/coap.cpp
@@ -1337,6 +1337,7 @@ Error CoapBase::SendNextBlock2Request(Request &aRequest, Msg &aRxMsg, uint32_t a
 
     requestBlockInfo = msgBlockInfo;
     requestBlockInfo.mBlockNumber++;
+    requestBlockInfo.mMoreBlocks = false; // RFC 7959 Section 2.3 second bullet: MUST be 0 in request.
 
     SuccessOrExit(error = PrepareNextBlockRequest(kOptionBlock2, aRequest, *request, requestBlockInfo));