diff --git a/netwerk/base/nsIUDPSocket.idl b/netwerk/base/nsIUDPSocket.idl
index 7063f6e4b39..00f8b9a328c 100644
--- a/netwerk/base/nsIUDPSocket.idl
+++ b/netwerk/base/nsIUDPSocket.idl
@@ -273,6 +273,13 @@ interface nsIUDPSocket : nsISupports
       */
     [noscript, notxpcom] void enableWritePoll();
 
+     /**
+      * isSocketClosed
+      *
+      * @return true when the socket is already closed.
+      */
+    [noscript, notxpcom] boolean isSocketClosed();
+
     /**
      * addOutputBytes
      *
diff --git a/netwerk/base/nsUDPSocket.cpp b/netwerk/base/nsUDPSocket.cpp
index 01320b6f183..d6b3e40acbd 100644
--- a/netwerk/base/nsUDPSocket.cpp
+++ b/netwerk/base/nsUDPSocket.cpp
@@ -1222,6 +1222,8 @@ void nsUDPSocket::EnableWritePoll() {
   mPollFlags = (PR_POLL_WRITE | PR_POLL_READ | PR_POLL_EXCEPT);
 }
 
+bool nsUDPSocket::IsSocketClosed() { return !!mFD; }
+
 NS_IMETHODIMP
 nsUDPSocket::SendBinaryStream(const nsACString& aHost, uint16_t aPort,
                               nsIInputStream* aStream) {
diff --git a/netwerk/protocol/http/Http3ConnectUDPStream.cpp b/netwerk/protocol/http/Http3ConnectUDPStream.cpp
index 5c4b433ad5d..09204741b61 100644
--- a/netwerk/protocol/http/Http3ConnectUDPStream.cpp
+++ b/netwerk/protocol/http/Http3ConnectUDPStream.cpp
@@ -266,6 +266,8 @@ int64_t Http3ConnectUDPStream::GetFileDescriptor() { return -1; }
 
 void Http3ConnectUDPStream::EnableWritePoll() {}
 
+bool Http3ConnectUDPStream::IsSocketClosed() { return mSendState == SEND_DONE; }
+
 void Http3ConnectUDPStream::AddOutputBytes(uint32_t aBytes) {}
 
 void Http3ConnectUDPStream::AddInputBytes(uint32_t aBytes) {}
diff --git a/netwerk/protocol/http/Http3Session.cpp b/netwerk/protocol/http/Http3Session.cpp
index c54a5c05a0c..7adfc143088 100644
--- a/netwerk/protocol/http/Http3Session.cpp
+++ b/netwerk/protocol/http/Http3Session.cpp
@@ -439,6 +439,11 @@ nsresult Http3Session::ProcessInput(nsIUDPSocket* socket) {
   LOG(("Http3Session::ProcessInput writer=%p [this=%p state=%d]",
        mUdpConn.get(), this, mState));
 
+  if (!socket || socket->IsSocketClosed()) {
+    MOZ_DIAGNOSTIC_ASSERT(false, "UDP socket should still be open");
+    return NS_ERROR_UNEXPECTED;
+  }
+
   if (mUseNSPRForIO) {
     while (true) {
       nsTArray<uint8_t> data;
@@ -1091,6 +1096,11 @@ nsresult Http3Session::ProcessOutput(nsIUDPSocket* socket) {
   LOG(("Http3Session::ProcessOutput reader=%p, [this=%p]", mUdpConn.get(),
        this));
 
+  if (!socket || socket->IsSocketClosed()) {
+    MOZ_DIAGNOSTIC_ASSERT(false, "UDP socket should still be open");
+    return NS_ERROR_UNEXPECTED;
+  }
+
   if (mUseNSPRForIO) {
     mSocket = socket;
     nsresult rv = mHttp3Connection->ProcessOutputAndSendUseNSPRForIO(
diff --git a/netwerk/protocol/http/HttpConnectionUDP.cpp b/netwerk/protocol/http/HttpConnectionUDP.cpp
index 08bc08ec288..9db11768d2c 100644
--- a/netwerk/protocol/http/HttpConnectionUDP.cpp
+++ b/netwerk/protocol/http/HttpConnectionUDP.cpp
@@ -619,6 +619,9 @@ void HttpConnectionUDP::Close(nsresult reason, bool aIsShutdown) {
     socket->Close();
   }
 
+  MOZ_DIAGNOSTIC_ASSERT(!mHttp3Session || mHttp3Session->IsClosed(),
+                        "Http3Session should already be closed");
+
   for (const auto& trans : mQueuedHttpConnectTransaction) {
     trans->Close(reason);
   }
@@ -718,7 +721,7 @@ nsresult HttpConnectionUDP::OnHeadersAvailable(nsAHttpTransaction* trans,
     // response headers so that it will be ready to receive the new response.
     if (mIsReused &&
         ((PR_IntervalNow() - mHttp3Session->LastWriteTime()) < k1000ms)) {
-      Close(NS_ERROR_NET_RESET);
+      CloseTransaction(mHttp3Session, NS_ERROR_NET_RESET);
       *reset = true;
       return NS_OK;
     }