diff --git a/src-input/duk_api_object.c b/src-input/duk_api_object.c
index dd771da3ae..1b2ab4ad57 100644
--- a/src-input/duk_api_object.c
+++ b/src-input/duk_api_object.c
@@ -625,12 +625,11 @@ DUK_EXTERNAL void duk_get_prototype(duk_context *ctx, duk_idx_t idx) {
 	obj = duk_require_hobject(ctx, idx);
 	DUK_ASSERT(obj != NULL);
 
-	/* XXX: shared helper for duk_push_hobject_or_undefined()? */
 	proto = DUK_HOBJECT_GET_PROTOTYPE(thr->heap, obj);
 	if (proto) {
 		duk_push_hobject(ctx, proto);
 	} else {
-		duk_push_undefined(ctx);
+		duk_push_null(ctx);
 	}
 }
 
@@ -643,7 +642,8 @@ DUK_EXTERNAL void duk_set_prototype(duk_context *ctx, duk_idx_t idx) {
 
 	obj = duk_require_hobject(ctx, idx);
 	DUK_ASSERT(obj != NULL);
-	duk_require_type_mask(ctx, -1, DUK_TYPE_MASK_UNDEFINED |
+	duk_require_type_mask(ctx, -1, DUK_TYPE_MASK_UNDEFINED |  /* FIXME: don't accept undefined anymore? */
+	                               DUK_TYPE_MASK_NULL |
 	                               DUK_TYPE_MASK_OBJECT);
 	proto = duk_get_hobject(ctx, -1);
 	/* proto can also be NULL here (allowed explicitly) */
diff --git a/website/api/duk_set_prototype.yaml b/website/api/duk_set_prototype.yaml
index 915a95a531..a693f797af 100644
--- a/website/api/duk_set_prototype.yaml
+++ b/website/api/duk_set_prototype.yaml
@@ -8,9 +8,9 @@ stack: |
 
 summary: |
   <p>Set the internal prototype of the value at <code>idx</code> to the value
-  at stack top (which must be an object or <code>undefined</code>).  If the
-  target value is not an object or the prototype value is not an object or
-  <code>undefined</code>, an error is thrown.</p>
+  at stack top If the target value is not an object or the prototype value is
+  not an object, <code>undefined</code>, or <code>null</code>, an error is
+  thrown.</p>
 
   <div class="note">
   Unlike Ecmascript prototype manipulation primitives, this API call allows