diff --git a/dlls/mshtml/htmlwindow.c b/dlls/mshtml/htmlwindow.c
index a4039ce08bc..731acd61cd7 100644
--- a/dlls/mshtml/htmlwindow.c
+++ b/dlls/mshtml/htmlwindow.c
@@ -3364,18 +3364,34 @@ static HRESULT WINAPI WindowDispEx_InvokeEx(IWineJSDispatchHost *iface, DISPID i
 static HRESULT WINAPI WindowDispEx_DeleteMemberByName(IWineJSDispatchHost *iface, BSTR bstrName, DWORD grfdex)
 {
     HTMLOuterWindow *This = impl_from_IWineJSDispatchHost(iface);
+    compat_mode_t compat_mode = dispex_compat_mode(&This->base.inner_window->event_target.dispex);
 
     TRACE("(%p)->(%s %lx)\n", This, debugstr_w(bstrName), grfdex);
 
+    if(compat_mode < COMPAT_MODE_IE8) {
+        /* Not implemented by IE */
+        return E_NOTIMPL;
+    }
+    if(compat_mode == COMPAT_MODE_IE8)
+        return MSHTML_E_INVALID_ACTION;
+
     return IWineJSDispatchHost_DeleteMemberByName(&This->base.inner_window->event_target.dispex.IWineJSDispatchHost_iface, bstrName, grfdex);
 }
 
 static HRESULT WINAPI WindowDispEx_DeleteMemberByDispID(IWineJSDispatchHost *iface, DISPID id)
 {
     HTMLOuterWindow *This = impl_from_IWineJSDispatchHost(iface);
+    compat_mode_t compat_mode = dispex_compat_mode(&This->base.inner_window->event_target.dispex);
 
     TRACE("(%p)->(%lx)\n", This, id);
 
+    if(compat_mode < COMPAT_MODE_IE8) {
+        /* Not implemented by IE */
+        return E_NOTIMPL;
+    }
+    if(compat_mode == COMPAT_MODE_IE8)
+        return MSHTML_E_INVALID_ACTION;
+
     return IWineJSDispatchHost_DeleteMemberByDispID(&This->base.inner_window->event_target.dispex.IWineJSDispatchHost_iface, id);
 }
 
diff --git a/dlls/mshtml/tests/documentmode.js b/dlls/mshtml/tests/documentmode.js
index ae5e68126dd..53372ac7752 100644
--- a/dlls/mshtml/tests/documentmode.js
+++ b/dlls/mshtml/tests/documentmode.js
@@ -1380,16 +1380,31 @@ sync_test("delete_prop", function() {
     /* test window object and its global scope handling */
     obj = window;
 
+    ok("encodeURIComponent" in obj, "encodeURIComponent not in obj");
+    try {
+        prop = window.encodeURIComponent;
+        r = (delete window.encodeURIComponent);
+        ok(v >= 9, "did not get an expect exception deleting encodeURIComponent");
+        ok(r, "delete returned " + r);
+        todo_wine.
+        ok(!("encodeURIComponent" in obj), "encodeURIComponent is still in obj");
+        window.encodeURIComponent = prop;
+    }catch(ex) {
+        ok(v < 9, "expected exception deleting encodeURIComponent");
+        ok(ex.number === 0xa01bd - 0x80000000, "deleting encodeURIComponent threw " + ex.number);
+        ok("encodeURIComponent" in obj, "encodeURIComponent is not in obj");
+    }
+
     obj.globalprop1 = true;
     ok(globalprop1, "globalprop1 = " + globalprop1);
     r = false;
     try {
         delete obj.globalprop1;
     }catch(ex) {
+        ok(ex.number === 0xa01bd - 0x80000000, "deleting globalprop1 threw " + ex.number);
         r = true;
     }
     if(v < 9) {
-        todo_wine.
         ok(r, "did not get an expected exception");
     }else {
         ok(!r, "got an unexpected globalprop1 exception");
@@ -1402,10 +1417,10 @@ sync_test("delete_prop", function() {
     try {
         delete obj.globalprop2;
     }catch(ex) {
+        ok(ex.number === 0xa01bd - 0x80000000, "deleting globalprop2 threw " + ex.number);
         r = true;
     }
     if(v < 9) {
-        todo_wine.
         ok(r, "did not get an expected globalprop2 exception");
     }else {
         ok(!r, "got an unexpected exception");
@@ -1419,12 +1434,11 @@ sync_test("delete_prop", function() {
     try {
         delete globalprop3;
     }catch(ex) {
+        ok(ex.number === 0xa01bd - 0x80000000, "deleting globalprop3 threw " + ex.number);
         r = true;
     }
     if(v < 9) {
-        todo_wine.
         ok(r, "did not get an expected exception");
-        todo_wine.
         ok("globalprop3" in obj, "globalprop3 is not in obj");
     }else {
         ok(!r, "got an unexpected globalprop3 exception");