diff --git a/Tests/test_imagemorph.py b/Tests/test_imagemorph.py
index 89a4022ae..cad3caebd 100644
--- a/Tests/test_imagemorph.py
+++ b/Tests/test_imagemorph.py
@@ -288,13 +288,13 @@ class MorphTests(PillowTestCase):
         imrgb = Image.new('RGB', (10, 10))
         iml = Image.new('L', (10, 10))
 
-        with self.assertRaises(ValueError):
+        with self.assertRaises(RuntimeError):
             _imagingmorph.apply(bytes(lut), imrgb.im.id, iml.im.id)
 
-        with self.assertRaises(ValueError):
+        with self.assertRaises(RuntimeError):
             _imagingmorph.apply(bytes(lut), iml.im.id, imrgb.im.id)
 
-        with self.assertRaises(ValueError):
+        with self.assertRaises(RuntimeError):
             _imagingmorph.match(bytes(lut), imrgb.im.id)
 
         # Should not raise
diff --git a/src/_imagingmorph.c b/src/_imagingmorph.c
index 0b60e4c80..b700f8482 100644
--- a/src/_imagingmorph.c
+++ b/src/_imagingmorph.c
@@ -66,12 +66,12 @@ apply(PyObject *self, PyObject* args)
 
     if (imgin->type != IMAGING_TYPE_UINT8 ||
         imgin->bands != 1) {
-        PyErr_SetString(PyExc_ValueError, "Unsupported image type");
+        PyErr_SetString(PyExc_RuntimeError, "Unsupported image type");
         return NULL;
     }
     if (imgout->type != IMAGING_TYPE_UINT8 ||
         imgout->bands != 1) {
-        PyErr_SetString(PyExc_ValueError, "Unsupported image type");
+        PyErr_SetString(PyExc_RuntimeError, "Unsupported image type");
         return NULL;
     }
 
@@ -169,7 +169,7 @@ match(PyObject *self, PyObject* args)
 
     if (imgin->type != IMAGING_TYPE_UINT8 ||
         imgin->bands != 1) {
-        PyErr_SetString(PyExc_ValueError, "Unsupported image type");
+        PyErr_SetString(PyExc_RuntimeError, "Unsupported image type");
         return NULL;
     }