diff --git a/src/corelib/platform/wasm/qstdweb.cpp b/src/corelib/platform/wasm/qstdweb.cpp
index 05121ba277..5d17069eec 100644
--- a/src/corelib/platform/wasm/qstdweb.cpp
+++ b/src/corelib/platform/wasm/qstdweb.cpp
@@ -10,6 +10,8 @@
 #include <emscripten/bind.h>
 #include <emscripten/emscripten.h>
 #include <emscripten/html5.h>
+#include <emscripten/threading.h>
+
 #include <cstdint>
 #include <iostream>
 
@@ -854,18 +856,33 @@ namespace Promise {
     }
 }
 
-bool haveAsyncify()
-{
-    static bool HaveAsyncify = jsHaveAsyncify();
-    return HaveAsyncify;
-}
-
+//  Asyncify and thread blocking: Normally, it's not possible to block the main
+//  thread, except if asyncify is enabled. Secondary threads can always block.
+//
+//  haveAsyncify(): returns true if the main thread can block on QEventLoop::exec(),
+//      if either asyncify 1 or 2 (JSPI) is available.
+//
+//  haveJspi(): returns true if asyncify 2 (JSPI) is available.
+//
+//  canBlockCallingThread(): returns true if the calling thread can block on 
+//      QEventLoop::exec(), using either asyncify or as a seconarday thread.
 bool haveJspi()
 {
     static bool HaveJspi = jsHaveJspi();
     return HaveJspi;
 }
 
+bool haveAsyncify()
+{
+    static bool HaveAsyncify = jsHaveAsyncify() || haveJspi();
+    return HaveAsyncify;
+}
+
+bool canBlockCallingThread()
+{
+    return haveAsyncify() || !emscripten_is_main_runtime_thread();
+}
+
 std::shared_ptr<CancellationFlag>
 readDataTransfer(emscripten::val webDataTransfer, std::function<QVariant(QByteArray)> imageReader,
                  std::function<void(std::unique_ptr<QMimeData>)> onDone)
diff --git a/src/corelib/platform/wasm/qstdweb_p.h b/src/corelib/platform/wasm/qstdweb_p.h
index a7a98ca042..7e94821272 100644
--- a/src/corelib/platform/wasm/qstdweb_p.h
+++ b/src/corelib/platform/wasm/qstdweb_p.h
@@ -215,6 +215,7 @@ namespace qstdweb {
 
     bool haveAsyncify();
     bool haveJspi();
+    bool canBlockCallingThread();
 
     struct CancellationFlag
     {