diff --git a/dlls/jscript/array.c b/dlls/jscript/array.c
index fb4982fb05f..190c7dc1508 100644
--- a/dlls/jscript/array.c
+++ b/dlls/jscript/array.c
@@ -188,7 +188,7 @@ static HRESULT concat_obj(jsdisp_t *array, IDispatch *obj, DWORD *len)
     jsdisp_t *jsobj;
     HRESULT hres;
 
-    jsobj = iface_to_jsdisp((IUnknown*)obj);
+    jsobj = iface_to_jsdisp(obj);
     if(jsobj) {
         if(is_class(jsobj, JSCLASS_ARRAY)) {
             hres = concat_array(array, (ArrayInstance*)jsobj, len);
@@ -695,7 +695,7 @@ static HRESULT Array_sort(script_ctx_t *ctx, vdisp_t *vthis, WORD flags, unsigne
             return E_FAIL;
         }
 
-        cmp_func = iface_to_jsdisp((IUnknown*)get_object(argv[0]));
+        cmp_func = iface_to_jsdisp(get_object(argv[0]));
         if(!cmp_func || !is_class(cmp_func, JSCLASS_FUNCTION)) {
             WARN("cmp_func is not a function\n");
             if(cmp_func)
diff --git a/dlls/jscript/dispex.c b/dlls/jscript/dispex.c
index 5efe0d5a121..93d74ba91cf 100644
--- a/dlls/jscript/dispex.c
+++ b/dlls/jscript/dispex.c
@@ -1014,7 +1014,7 @@ HRESULT init_dispex_from_constr(jsdisp_t *dispex, script_ctx_t *ctx, const built
         }
 
         if(is_object_instance(val))
-            prot = iface_to_jsdisp((IUnknown*)get_object(val));
+            prot = iface_to_jsdisp(get_object(val));
         jsval_release(val);
     }
 
@@ -1025,12 +1025,12 @@ HRESULT init_dispex_from_constr(jsdisp_t *dispex, script_ctx_t *ctx, const built
     return hres;
 }
 
-jsdisp_t *iface_to_jsdisp(IUnknown *iface)
+jsdisp_t *iface_to_jsdisp(IDispatch *iface)
 {
     jsdisp_t *ret;
     HRESULT hres;
 
-    hres = IUnknown_QueryInterface(iface, &IID_IDispatchJS, (void**)&ret);
+    hres = IDispatch_QueryInterface(iface, &IID_IDispatchJS, (void**)&ret);
     if(FAILED(hres))
         return NULL;
 
@@ -1114,7 +1114,7 @@ HRESULT disp_call(script_ctx_t *ctx, IDispatch *disp, DISPID id, WORD flags, uns
     unsigned i;
     HRESULT hres;
 
-    jsdisp = iface_to_jsdisp((IUnknown*)disp);
+    jsdisp = iface_to_jsdisp(disp);
     if(jsdisp) {
         if(flags & DISPATCH_PROPERTYPUT) {
             FIXME("disp_call(propput) on builtin object\n");
@@ -1207,7 +1207,7 @@ HRESULT disp_call_value(script_ctx_t *ctx, IDispatch *disp, IDispatch *jsthis, W
 
     assert(!(flags & ~(DISPATCH_METHOD|DISPATCH_CONSTRUCT|DISPATCH_JSCRIPT_INTERNAL_MASK)));
 
-    jsdisp = iface_to_jsdisp((IUnknown*)disp);
+    jsdisp = iface_to_jsdisp(disp);
     if(jsdisp) {
         hres = jsdisp_call_value(jsdisp, jsthis, flags, argc, argv, r);
         jsdisp_release(jsdisp);
@@ -1346,7 +1346,7 @@ HRESULT disp_propput(script_ctx_t *ctx, IDispatch *disp, DISPID id, jsval_t val)
     jsdisp_t *jsdisp;
     HRESULT hres;
 
-    jsdisp = iface_to_jsdisp((IUnknown*)disp);
+    jsdisp = iface_to_jsdisp(disp);
     if(jsdisp) {
         dispex_prop_t *prop;
 
@@ -1451,7 +1451,7 @@ HRESULT disp_propget(script_ctx_t *ctx, IDispatch *disp, DISPID id, jsval_t *val
     VARIANT var;
     HRESULT hres;
 
-    jsdisp = iface_to_jsdisp((IUnknown*)disp);
+    jsdisp = iface_to_jsdisp(disp);
     if(jsdisp) {
         hres = jsdisp_propget(jsdisp, id, val);
         jsdisp_release(jsdisp);
@@ -1502,7 +1502,7 @@ HRESULT disp_delete(IDispatch *disp, DISPID id, BOOL *ret)
     jsdisp_t *jsdisp;
     HRESULT hres;
 
-    jsdisp = iface_to_jsdisp((IUnknown*)disp);
+    jsdisp = iface_to_jsdisp(disp);
     if(jsdisp) {
         dispex_prop_t *prop;
 
@@ -1538,7 +1538,7 @@ HRESULT disp_delete_name(script_ctx_t *ctx, IDispatch *disp, jsstr_t *name, BOOL
     BSTR bstr;
     HRESULT hres;
 
-    jsdisp = iface_to_jsdisp((IUnknown*)disp);
+    jsdisp = iface_to_jsdisp(disp);
     if(jsdisp) {
         dispex_prop_t *prop;
         const WCHAR *ptr;
diff --git a/dlls/jscript/engine.c b/dlls/jscript/engine.c
index 74cef15e400..28c4b8d3828 100644
--- a/dlls/jscript/engine.c
+++ b/dlls/jscript/engine.c
@@ -314,7 +314,7 @@ static HRESULT disp_get_id(script_ctx_t *ctx, IDispatch *disp, const WCHAR *name
     BSTR bstr;
     HRESULT hres;
 
-    jsdisp = iface_to_jsdisp((IUnknown*)disp);
+    jsdisp = iface_to_jsdisp(disp);
     if(jsdisp) {
         hres = jsdisp_get_id(jsdisp, name, flags, id);
         jsdisp_release(jsdisp);
@@ -1321,7 +1321,7 @@ static HRESULT interp_instanceof(script_ctx_t *ctx)
         return throw_type_error(ctx, JS_E_FUNCTION_EXPECTED, NULL);
     }
 
-    obj = iface_to_jsdisp((IUnknown*)get_object(v));
+    obj = iface_to_jsdisp(get_object(v));
     IDispatch_Release(get_object(v));
     if(!obj) {
         FIXME("non-jsdisp objects not supported\n");
@@ -1341,7 +1341,7 @@ static HRESULT interp_instanceof(script_ctx_t *ctx)
 
     if(is_object_instance(prot)) {
         if(is_object_instance(v))
-            tmp = iface_to_jsdisp((IUnknown*)get_object(v));
+            tmp = iface_to_jsdisp(get_object(v));
         for(iter = tmp; !ret && iter; iter = iter->prototype) {
             hres = disp_cmp(get_object(prot), to_disp(iter), &ret);
             if(FAILED(hres))
@@ -1643,7 +1643,7 @@ static HRESULT typeof_string(jsval_t v, const WCHAR **ret)
     case JSV_OBJECT: {
         jsdisp_t *dispex;
 
-        if(get_object(v) && (dispex = iface_to_jsdisp((IUnknown*)get_object(v)))) {
+        if(get_object(v) && (dispex = iface_to_jsdisp(get_object(v)))) {
             *ret = is_class(dispex, JSCLASS_FUNCTION) ? functionW : objectW;
             jsdisp_release(dispex);
         }else {
@@ -2587,7 +2587,7 @@ HRESULT exec_source(script_ctx_t *ctx, DWORD flags, bytecode_t *bytecode, functi
     if(this_obj) {
         jsdisp_t *jsthis;
 
-        jsthis = iface_to_jsdisp((IUnknown*)this_obj);
+        jsthis = iface_to_jsdisp(this_obj);
         if(jsthis) {
             if(jsthis->builtin_info->class == JSCLASS_GLOBAL || jsthis->builtin_info->class == JSCLASS_NONE)
                 this_obj = NULL;
diff --git a/dlls/jscript/function.c b/dlls/jscript/function.c
index 6817aa7e864..361b5cbc89e 100644
--- a/dlls/jscript/function.c
+++ b/dlls/jscript/function.c
@@ -441,7 +441,7 @@ static HRESULT Function_apply(script_ctx_t *ctx, vdisp_t *jsthis, WORD flags, un
         jsdisp_t *arg_array = NULL;
 
         if(is_object_instance(argv[1])) {
-            arg_array = iface_to_jsdisp((IUnknown*)get_object(argv[1]));
+            arg_array = iface_to_jsdisp(get_object(argv[1]));
             if(arg_array &&
                (!is_class(arg_array, JSCLASS_ARRAY) && !is_class(arg_array, JSCLASS_ARGUMENTS) )) {
                 jsdisp_release(arg_array);
diff --git a/dlls/jscript/jscript.h b/dlls/jscript/jscript.h
index 4331ee7c5fa..2ca24375ce7 100644
--- a/dlls/jscript/jscript.h
+++ b/dlls/jscript/jscript.h
@@ -128,7 +128,7 @@ typedef enum {
     JSCLASS_JSON
 } jsclass_t;
 
-jsdisp_t *iface_to_jsdisp(IUnknown*) DECLSPEC_HIDDEN;
+jsdisp_t *iface_to_jsdisp(IDispatch*) DECLSPEC_HIDDEN;
 
 typedef struct {
     union {
@@ -170,7 +170,7 @@ static inline void set_disp(vdisp_t *vdisp, IDispatch *disp)
     jsdisp_t *jsdisp;
     HRESULT hres;
 
-    jsdisp = iface_to_jsdisp((IUnknown*)disp);
+    jsdisp = iface_to_jsdisp(disp);
     if(jsdisp) {
         vdisp->u.jsdisp = jsdisp;
         vdisp->flags = VDISP_JSDISP | VDISP_DISPEX;
diff --git a/dlls/jscript/json.c b/dlls/jscript/json.c
index 25f620e8e42..7d69cf55ad9 100644
--- a/dlls/jscript/json.c
+++ b/dlls/jscript/json.c
@@ -421,7 +421,7 @@ static HRESULT maybe_to_primitive(script_ctx_t *ctx, jsval_t val, jsval_t *r)
     jsdisp_t *obj;
     HRESULT hres;
 
-    if(!is_object_instance(val) || !get_object(val) || !(obj = iface_to_jsdisp((IUnknown*)get_object(val))))
+    if(!is_object_instance(val) || !get_object(val) || !(obj = iface_to_jsdisp(get_object(val))))
         return jsval_copy(val, r);
 
     if(is_class(obj, JSCLASS_NUMBER)) {
@@ -672,7 +672,7 @@ static HRESULT stringify(stringify_ctx_t *ctx, jsval_t val)
         jsdisp_t *obj;
         DISPID id;
 
-        obj = iface_to_jsdisp((IUnknown*)get_object(val));
+        obj = iface_to_jsdisp(get_object(val));
         if(!obj)
             return S_FALSE;
 
@@ -730,7 +730,7 @@ static HRESULT stringify(stringify_ctx_t *ctx, jsval_t val)
     case JSV_OBJECT: {
         jsdisp_t *obj;
 
-        obj = iface_to_jsdisp((IUnknown*)get_object(value));
+        obj = iface_to_jsdisp(get_object(value));
         if(!obj) {
             hres = S_FALSE;
             break;
diff --git a/dlls/jscript/jsregexp.c b/dlls/jscript/jsregexp.c
index e4fae220b3d..9f74e50196c 100644
--- a/dlls/jscript/jsregexp.c
+++ b/dlls/jscript/jsregexp.c
@@ -704,7 +704,7 @@ HRESULT create_regexp_var(script_ctx_t *ctx, jsval_t src_arg, jsval_t *flags_arg
     if(is_object_instance(src_arg)) {
         jsdisp_t *obj;
 
-        obj = iface_to_jsdisp((IUnknown*)get_object(src_arg));
+        obj = iface_to_jsdisp(get_object(src_arg));
         if(obj) {
             if(is_class(obj, JSCLASS_REGEXP)) {
                 RegExpInstance *regexp = (RegExpInstance*)obj;
@@ -955,7 +955,7 @@ static HRESULT RegExpConstr_value(script_ctx_t *ctx, vdisp_t *jsthis, WORD flags
     case DISPATCH_METHOD:
         if(argc) {
             if(is_object_instance(argv[0])) {
-                jsdisp_t *jsdisp = iface_to_jsdisp((IUnknown*)get_object(argv[0]));
+                jsdisp_t *jsdisp = iface_to_jsdisp(get_object(argv[0]));
                 if(jsdisp) {
                     if(is_class(jsdisp, JSCLASS_REGEXP)) {
                         if(argc > 1 && !is_undefined(argv[1])) {
diff --git a/dlls/jscript/jsutils.c b/dlls/jscript/jsutils.c
index 447b7c6a63b..dd7951067af 100644
--- a/dlls/jscript/jsutils.c
+++ b/dlls/jscript/jsutils.c
@@ -392,7 +392,7 @@ HRESULT to_primitive(script_ctx_t *ctx, jsval_t val, jsval_t *ret, hint_t hint)
             return S_OK;
         }
 
-        jsdisp = iface_to_jsdisp((IUnknown*)get_object(val));
+        jsdisp = iface_to_jsdisp(get_object(val));
         if(!jsdisp)
             return disp_propget(ctx, get_object(val), DISPID_VALUE, ret);
 
diff --git a/dlls/jscript/string.c b/dlls/jscript/string.c
index 582a289d39e..9b6b5ff3fe9 100644
--- a/dlls/jscript/string.c
+++ b/dlls/jscript/string.c
@@ -636,7 +636,7 @@ static HRESULT String_match(script_ctx_t *ctx, vdisp_t *jsthis, WORD flags, unsi
     }
 
     if(is_object_instance(argv[0])) {
-        regexp = iface_to_jsdisp((IUnknown*)get_object(argv[0]));
+        regexp = iface_to_jsdisp(get_object(argv[0]));
         if(regexp && !is_class(regexp, JSCLASS_REGEXP)) {
             jsdisp_release(regexp);
             regexp = NULL;
@@ -799,7 +799,7 @@ static HRESULT String_replace(script_ctx_t *ctx, vdisp_t *jsthis, WORD flags, un
     }
 
     if(is_object_instance(argv[0])) {
-        regexp = iface_to_jsdisp((IUnknown*)get_object(argv[0]));
+        regexp = iface_to_jsdisp(get_object(argv[0]));
         if(regexp && !is_class(regexp, JSCLASS_REGEXP)) {
             jsdisp_release(regexp);
             regexp = NULL;
@@ -816,7 +816,7 @@ static HRESULT String_replace(script_ctx_t *ctx, vdisp_t *jsthis, WORD flags, un
 
     if(argc >= 2) {
         if(is_object_instance(argv[1])) {
-            rep_func = iface_to_jsdisp((IUnknown*)get_object(argv[1]));
+            rep_func = iface_to_jsdisp(get_object(argv[1]));
             if(rep_func && !is_class(rep_func, JSCLASS_FUNCTION)) {
                 jsdisp_release(rep_func);
                 rep_func = NULL;
@@ -1017,7 +1017,7 @@ static HRESULT String_search(script_ctx_t *ctx, vdisp_t *jsthis, WORD flags, uns
     }
 
     if(is_object_instance(argv[0])) {
-        regexp = iface_to_jsdisp((IUnknown*)get_object(argv[0]));
+        regexp = iface_to_jsdisp(get_object(argv[0]));
         if(regexp && !is_class(regexp, JSCLASS_REGEXP)) {
             jsdisp_release(regexp);
             regexp = NULL;
@@ -1161,7 +1161,7 @@ static HRESULT String_split(script_ctx_t *ctx, vdisp_t *jsthis, WORD flags, unsi
     }
 
     if(is_object_instance(argv[0])) {
-        regexp = iface_to_jsdisp((IUnknown*)get_object(argv[0]));
+        regexp = iface_to_jsdisp(get_object(argv[0]));
         if(regexp) {
             if(!is_class(regexp, JSCLASS_REGEXP)) {
                 jsdisp_release(regexp);