diff --git a/src/encode.c b/src/encode.c
index 72ad3fa07..620774f67 100644
--- a/src/encode.c
+++ b/src/encode.c
@@ -722,7 +722,10 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) {
         }
 
         if (!is_core_tag) {
-            PyObject *tag_type = PyDict_GetItem(types, key);
+            PyObject *tag_type;
+            if (PyDict_GetItemRef(types, key, &tag_type) == 0) {
+                PyErr_SetString(PyExc_KeyError, "unknown tag type");
+            }
             if (tag_type) {
                 int type_int = PyLong_AsLong(tag_type);
                 if (type_int >= TIFF_BYTE && type_int <= TIFF_DOUBLE) {