diff --git a/src/qpython.cpp b/src/qpython.cpp
index 72c6885..4cefcad 100644
--- a/src/qpython.cpp
+++ b/src/qpython.cpp
@@ -186,7 +186,15 @@ QPython::call_sync(QString func, QVariant args)
         QVariant v;
 
         PyObject *argl = convertQVariantToPyObject(args);
-        assert(PyList_Check(argl));
+        if (!PyList_Check(argl)) {
+            Py_DECREF(callable);
+            Py_XDECREF(argl);
+            emit error(QString("Not a parameter list in call to %1: %2")
+                    .arg(func).arg(args.toString()));
+            priv->leave();
+            return QVariant();
+        }
+
         PyObject *argt = PyList_AsTuple(argl);
         Py_DECREF(argl);
         PyObject *o = PyObject_Call(callable, argt, NULL);
diff --git a/tests/test_callparam/test_callparam.qml b/tests/test_callparam/test_callparam.qml
new file mode 100644
index 0000000..49ec12f
--- /dev/null
+++ b/tests/test_callparam/test_callparam.qml
@@ -0,0 +1,27 @@
+import QtQuick 2.0
+import io.thp.pyotherside 1.0
+
+Rectangle {
+    id: page
+    width: 300
+    height: 300
+
+    Python {
+        Component.onCompleted: {
+            // We use call_sync() instead of call() in order
+            // to guarantee the right ordering of Python's output
+            // and the output of the JS engine for the error
+
+            // This should fail with an error:
+            // "Not a parameter list in call to print: 123"
+            call_sync('print', 123);
+
+            // This should work and print "123" on the console
+            call_sync('print', [123]);
+        }
+
+        onError: {
+            console.log('Received error: ' + traceback);
+        }
+    }
+}