diff --git a/src/mesh/RadioInterface.cpp b/src/mesh/RadioInterface.cpp
index f616e866a42..b7dbf5bb54d 100644
--- a/src/mesh/RadioInterface.cpp
+++ b/src/mesh/RadioInterface.cpp
@@ -1462,10 +1462,18 @@ void RadioInterface::deliverToReceiver(meshtastic_MeshPacket *p)
  */
 size_t RadioInterface::beginSending(meshtastic_MeshPacket *p)
 {
-    assert(!sendingPacket);
-
-    // LOG_DEBUG("Send queued packet on mesh (txGood=%d,rxGood=%d,rxBad=%d)", rf95.txGood(), rf95.rxGood(), rf95.rxBad());
-    assert(p->which_payload_variant == meshtastic_MeshPacket_encrypted_tag); // It should have already been encoded by now
+    // These used to be asserts, which hang forever with no diagnostic on STM32WL. Reject and release
+    // instead - the caller must treat a 0 return as "not sent, p already released".
+    if (sendingPacket) {
+        LOG_ERROR("beginSending called while a send is already in progress");
+        packetPool.release(p);
+        return 0;
+    }
+    if (p->which_payload_variant != meshtastic_MeshPacket_encrypted_tag) {
+        LOG_ERROR("beginSending called with an unencrypted packet");
+        packetPool.release(p);
+        return 0;
+    }
 
     radioBuffer.header.from = p->from;
     radioBuffer.header.to = p->to;
@@ -1482,8 +1490,17 @@ size_t RadioInterface::beginSending(meshtastic_MeshPacket *p)
     radioBuffer.header.flags |= (p->hop_start << PACKET_FLAGS_HOP_START_SHIFT) & PACKET_FLAGS_HOP_START_MASK;
 
     // if the sender nodenum is zero, that means uninitialized
-    assert(radioBuffer.header.from);
-    assert(p->encrypted.size <= sizeof(radioBuffer.payload));
+    if (!radioBuffer.header.from) {
+        LOG_ERROR("beginSending called with an unset sender node num");
+        packetPool.release(p);
+        return 0;
+    }
+    if (p->encrypted.size > sizeof(radioBuffer.payload)) {
+        LOG_ERROR("beginSending: encrypted size %u exceeds radio buffer capacity %zu", p->encrypted.size,
+                  sizeof(radioBuffer.payload));
+        packetPool.release(p);
+        return 0;
+    }
     memcpy(radioBuffer.payload, p->encrypted.bytes, p->encrypted.size);
 
     sendingPacket = p;
diff --git a/src/mesh/RadioLibInterface.cpp b/src/mesh/RadioLibInterface.cpp
index 5a9b292cda8..c34fadabc19 100644
--- a/src/mesh/RadioLibInterface.cpp
+++ b/src/mesh/RadioLibInterface.cpp
@@ -773,6 +773,8 @@ bool RadioLibInterface::startSend(meshtastic_MeshPacket *txp)
         configHardwareForSend(); // must be after setStandby
 
         size_t numbytes = beginSending(txp);
+        if (numbytes == 0) // beginSending() already released txp and logged why
+            return false;
 
         int res = iface->startTransmit((uint8_t *)&radioBuffer, numbytes);
         if (res != RADIOLIB_ERR_NONE) {
diff --git a/src/platform/portduino/SimRadio.cpp b/src/platform/portduino/SimRadio.cpp
index 2786903ebbb..bb6433d0b74 100644
--- a/src/platform/portduino/SimRadio.cpp
+++ b/src/platform/portduino/SimRadio.cpp
@@ -208,6 +208,8 @@ void SimRadio::startSend(meshtastic_MeshPacket *txp)
     printPacket("Start low level send", txp);
     isReceiving = false;
     size_t numbytes = beginSending(txp);
+    if (numbytes == 0) // beginSending() already released txp and logged why
+        return;
     meshtastic_MeshPacket *p = packetPool.allocCopy(*txp);
     if (!p)
         return;