diff --git a/include/wx/private/webrequest_curl.h b/include/wx/private/webrequest_curl.h
index f31adb806f..b16481bb1d 100644
--- a/include/wx/private/webrequest_curl.h
+++ b/include/wx/private/webrequest_curl.h
@@ -145,8 +145,13 @@ private:
     wxMutex m_mutex;
     wxCondition m_condition;
     bool m_shuttingDown;
-    wxMutex m_cancelledMutex;
-    wxVector< wxObjectDataPtr<wxWebRequestCURL> > m_cancelledRequests;
+
+    // MT-safe vector of requests for which Cancel() was called.
+    struct CancelledData
+    {
+        wxCriticalSection cs;
+        wxVector< wxObjectDataPtr<wxWebRequestCURL> > requests;
+    } m_cancelled;
 
     static int ms_activeSessions;
 
diff --git a/src/common/webrequest_curl.cpp b/src/common/webrequest_curl.cpp
index 73f4e4c1c8..4ee6980d0f 100644
--- a/src/common/webrequest_curl.cpp
+++ b/src/common/webrequest_curl.cpp
@@ -448,11 +448,11 @@ wxThread::ExitCode wxWebSessionCURL::Entry()
     {
         // Handle cancelled requests
         {
-            wxMutexLocker lock(m_cancelledMutex);
-            while ( !m_cancelledRequests.empty() )
+            wxCriticalSectionLocker lock(m_cancelled.cs);
+            while ( !m_cancelled.requests.empty() )
             {
-                wxObjectDataPtr<wxWebRequestCURL> request(m_cancelledRequests.back());
-                m_cancelledRequests.pop_back();
+                wxObjectDataPtr<wxWebRequestCURL> request(m_cancelled.requests.back());
+                m_cancelled.requests.pop_back();
                 curl_multi_remove_handle(m_handle, request->GetHandle());
                 request->SetState(wxWebRequest::State_Cancelled);
             }
@@ -527,9 +527,9 @@ void wxWebSessionCURL::CancelRequest(wxWebRequestCURL* request)
 {
     // Add the request to a list of threads that will be removed from the curl
     // multi handle in the worker thread
-    wxMutexLocker lock(m_cancelledMutex);
+    wxCriticalSectionLocker lock(m_cancelled.cs);
     request->IncRef();
-    m_cancelledRequests.push_back(wxObjectDataPtr<wxWebRequestCURL>(request));
+    m_cancelled.requests.push_back(wxObjectDataPtr<wxWebRequestCURL>(request));
 }
 
 wxVersionInfo  wxWebSessionCURL::GetLibraryVersionInfo()