diff --git a/dlls/mshtml/tests/xmlhttprequest.c b/dlls/mshtml/tests/xmlhttprequest.c
index 0db5cb9717b..868035d0419 100644
--- a/dlls/mshtml/tests/xmlhttprequest.c
+++ b/dlls/mshtml/tests/xmlhttprequest.c
@@ -522,16 +522,21 @@ static void test_responseXML(const WCHAR *expect_text)
     IDispatch_Release(disp);
 }
 
-#define xhr_open(a,b) _xhr_open(__LINE__,a,b)
-static HRESULT _xhr_open(unsigned line, const WCHAR *url_w, const WCHAR *method_w)
+#define xhr_open(a,b,c) _xhr_open(__LINE__,a,b,c)
+static HRESULT _xhr_open(unsigned line, const WCHAR *url_w, const WCHAR *method_w, BOOL use_bool)
 {
     BSTR method = SysAllocString(method_w);
     BSTR url = SysAllocString(url_w);
     VARIANT async, empty;
     HRESULT hres;
 
-    V_VT(&async) = VT_BOOL;
-    V_BOOL(&async) = VARIANT_TRUE;
+    if(use_bool) {
+        V_VT(&async) = VT_BOOL;
+        V_BOOL(&async) = VARIANT_TRUE;
+    }else {
+        V_VT(&async) = VT_I4;
+        V_I4(&async) = 1;
+    }
     V_VT(&empty) = VT_EMPTY;
 
     hres = IHTMLXMLHttpRequest_open(xhr, method, url, async, empty, empty);
@@ -787,7 +792,7 @@ static void test_async_xhr(IHTMLDocument2 *doc, const WCHAR *xml_url, const WCHA
     ok(val == 0, "Expect UNSENT, got %ld\n", val);
 
     SET_EXPECT(xmlhttprequest_onreadystatechange_opened);
-    hres = xhr_open(xml_url, L"GET");
+    hres = xhr_open(xml_url, L"GET", TRUE);
     CHECK_CALLED(xmlhttprequest_onreadystatechange_opened);
 
     if(FAILED(hres)) {
@@ -898,7 +903,7 @@ static void test_async_xhr_abort(IHTMLDocument2 *doc, const WCHAR *xml_url)
     hres = IHTMLXMLHttpRequest_put_onreadystatechange(xhr, var);
 
     SET_EXPECT(xmlhttprequest_onreadystatechange_opened);
-    xhr_open(xml_url, L"GET");
+    xhr_open(xml_url, L"GET", TRUE);
     CHECK_CALLED(xmlhttprequest_onreadystatechange_opened);
 
     hres = IHTMLXMLHttpRequest_abort(xhr);
@@ -922,7 +927,7 @@ static void test_async_xhr_abort(IHTMLDocument2 *doc, const WCHAR *xml_url)
     hres = IHTMLXMLHttpRequest_put_onreadystatechange(xhr, var);
 
     SET_EXPECT(xmlhttprequest_onreadystatechange_opened);
-    xhr_open(xml_url, L"GET");
+    xhr_open(xml_url, L"GET", FALSE);
     CHECK_CALLED(xmlhttprequest_onreadystatechange_opened);
 
     loading_cnt = 0;
@@ -969,7 +974,7 @@ static void test_xhr_post(IHTMLDocument2 *doc)
     ok(hres == S_OK, "put_onreadystatechange failed: %08lx\n", hres);
 
     SET_EXPECT(xmlhttprequest_onreadystatechange_opened);
-    xhr_open(L"http://test.winehq.org/tests/post.php", L"POST");
+    xhr_open(L"http://test.winehq.org/tests/post.php", L"POST", FALSE);
     CHECK_CALLED(xmlhttprequest_onreadystatechange_opened);
 
     set_request_header(xhr, L"Content-Type", L"application/x-www-form-urlencoded");
diff --git a/dlls/mshtml/xmlhttprequest.c b/dlls/mshtml/xmlhttprequest.c
index 0ae69df3bda..17219593026 100644
--- a/dlls/mshtml/xmlhttprequest.c
+++ b/dlls/mshtml/xmlhttprequest.c
@@ -508,8 +508,12 @@ static HRESULT WINAPI HTMLXMLHttpRequest_open(IHTMLXMLHttpRequest *iface, BSTR b
     TRACE("(%p)->(%s %s %s %s %s)\n", This, debugstr_w(bstrMethod), debugstr_w(bstrUrl), debugstr_variant(&varAsync), debugstr_variant(&varUser), debugstr_variant(&varPassword));
 
     if(V_VT(&varAsync) != VT_BOOL) {
-        FIXME("varAsync not supported: %s\n", debugstr_variant(&varAsync));
-        return E_FAIL;
+        LCID lcid = MAKELCID(MAKELANGID(LANG_ENGLISH,SUBLANG_ENGLISH_US),SORT_DEFAULT);
+        hres = VariantChangeTypeEx(&varAsync, &varAsync, lcid, 0, VT_BOOL);
+        if(FAILED(hres)) {
+            WARN("Failed to convert varAsync to BOOL: %#lx\n", hres);
+            return hres;
+        }
     }
 
     /* Note: Starting with Gecko 30.0 (Firefox 30.0 / Thunderbird 30.0 / SeaMonkey 2.27),