diff --git a/dlls/mshtml/htmlwindow.c b/dlls/mshtml/htmlwindow.c
index c5c2e784ff3..40df40c9979 100644
--- a/dlls/mshtml/htmlwindow.c
+++ b/dlls/mshtml/htmlwindow.c
@@ -177,8 +177,27 @@ static HRESULT WINAPI HTMLWindow2_item(IHTMLWindow2 *iface, VARIANT *pvarIndex,
 static HRESULT WINAPI HTMLWindow2_get_length(IHTMLWindow2 *iface, LONG *p)
 {
     HTMLWindow *This = HTMLWINDOW2_THIS(iface);
-    FIXME("(%p)->(%p)\n", This, p);
-    return E_NOTIMPL;
+    nsIDOMWindowCollection *nscollection;
+    PRUint32 length;
+    nsresult nsres;
+
+    TRACE("(%p)->(%p)\n", This, p);
+
+    nsres = nsIDOMWindow_GetFrames(This->nswindow, &nscollection);
+    if(NS_FAILED(nsres)) {
+        ERR("GetFrames failed: %08x\n", nsres);
+        return E_FAIL;
+    }
+
+    nsres = nsIDOMWindowCollection_GetLength(nscollection, &length);
+    nsIDOMWindowCollection_Release(nscollection);
+    if(NS_FAILED(nsres)) {
+        ERR("GetLength failed: %08x\n", nsres);
+        return E_FAIL;
+    }
+
+    *p = length;
+    return S_OK;
 }
 
 static HRESULT WINAPI HTMLWindow2_get_frames(IHTMLWindow2 *iface, IHTMLFramesCollection2 **p)
diff --git a/dlls/mshtml/nsiface.idl b/dlls/mshtml/nsiface.idl
index 571c0230b09..7429c60d3a0 100644
--- a/dlls/mshtml/nsiface.idl
+++ b/dlls/mshtml/nsiface.idl
@@ -89,6 +89,7 @@ interface nsIDocumentStateListener;
 interface nsIDOMCSSStyleSheet;
 interface nsIDOMDocumentView;
 interface nsIDocumentObserver;
+interface nsIDOMWindow;
 
 interface IMoniker;
 
@@ -109,7 +110,6 @@ typedef nsISupports nsISHistory;
 typedef nsISupports nsIWidget;
 typedef nsISupports nsIHttpHeaderVisitor;
 typedef nsISupports nsIDOMBarProp;
-typedef nsISupports nsIDOMWindowCollection;
 typedef nsISupports nsIPrompt;
 typedef nsISupports nsIAuthPrompt;
 typedef nsISupports nsIDOMNamedNodeMap;
@@ -1106,6 +1106,19 @@ interface nsISelection : nsISupports
     nsresult ToString(PRUnichar **_retval);
 }
 
+[
+    object,
+    uuid(a6cf906f-15b3-11d2-932e-00805f8add32),
+    local
+    /* FROZEN */
+]
+interface nsIDOMWindowCollection : nsISupports
+{
+    nsresult GetLength(PRUint32 *aLength);
+    nsresult Item(PRUint32 index, nsIDOMWindow **_retval);
+    nsresult NamedItem(const nsAString *name, nsIDOMWindow **_retval);
+}
+
 [
     object,
     uuid(a6cf906b-15b3-11d2-932e-00805f8add32),
diff --git a/dlls/mshtml/tests/dom.c b/dlls/mshtml/tests/dom.c
index bb974295971..f826a0177c1 100644
--- a/dlls/mshtml/tests/dom.c
+++ b/dlls/mshtml/tests/dom.c
@@ -851,6 +851,16 @@ static void _set_window_name(unsigned line, IHTMLWindow2 *window, const char *na
     _test_window_name(line, window, name);
 }
 
+#define test_window_length(w,l) _test_window_length(__LINE__,w,l)
+static void _test_window_length(unsigned line, IHTMLWindow2 *window, LONG exlen)
+{
+    LONG length = -1;
+    HRESULT hres;
+
+    hres = IHTMLWindow2_get_length(window, &length);
+    ok_(__FILE__,line)(hres == S_OK, "get_length failed: %08x\n", hres);
+    ok_(__FILE__,line)(length == exlen, "length = %d, expected %d\n", length, exlen);
+}
 
 static void test_get_set_attr(IHTMLDocument2 *doc)
 {
@@ -4414,6 +4424,7 @@ static void test_window(IHTMLDocument2 *doc)
 
     test_window_name(window, NULL);
     set_window_name(window, "test");
+    test_window_length(window, 0);
 
     IHTMLWindow2_Release(window);
 }
@@ -4648,6 +4659,8 @@ static void test_iframe_elem(IHTMLElement *elem)
     ok(hres == S_OK, "get_contentWindow failed: %08x\n", hres);
     ok(content_window != NULL, "contentWindow = NULL\n");
 
+    test_window_length(content_window, 0);
+
     content_doc = NULL;
     hres = IHTMLWindow2_get_document(content_window, &content_doc);
     IHTMLWindow2_Release(content_window);
@@ -5202,6 +5215,7 @@ static void test_elems(IHTMLDocument2 *doc)
     window = get_doc_window(doc);
     test_window_name(window, NULL);
     set_window_name(window, "test name");
+    test_window_length(window, 1);
     IHTMLWindow2_Release(window);
 }