diff --git a/Tests/test_imagefile.py b/Tests/test_imagefile.py
index 372cee8c0..a5c76700d 100644
--- a/Tests/test_imagefile.py
+++ b/Tests/test_imagefile.py
@@ -82,6 +82,19 @@ class TestImageFile:
             p.feed(data)
             assert (48, 48) == p.image.size
 
+    @skip_unless_feature("webp")
+    @skip_unless_feature("webp_anim")
+    def test_incremental_webp(self):
+        with ImageFile.Parser() as p:
+            with open("Tests/images/hopper.webp", "rb") as f:
+                p.feed(f.read(1024))
+
+                # Check that insufficient data was given in the first feed
+                assert not p.image
+
+                p.feed(f.read())
+            assert (128, 128) == p.image.size
+
     @skip_unless_feature("zlib")
     def test_safeblock(self):
         im1 = hopper()
diff --git a/src/_webp.c b/src/_webp.c
index bccfb3d89..fd99116cb 100644
--- a/src/_webp.c
+++ b/src/_webp.c
@@ -396,7 +396,7 @@ _anim_decoder_new(PyObject *self, PyObject *args) {
         }
         PyObject_Del(decp);
     }
-    PyErr_SetString(PyExc_RuntimeError, "could not create decoder object");
+    PyErr_SetString(PyExc_OSError, "could not create decoder object");
     return NULL;
 }