diff --git a/NEWS b/NEWS
index 9216010e..51830ff1 100644
--- a/NEWS
+++ b/NEWS
@@ -10,6 +10,12 @@ Bug fixes:
   (:ticket:`#191`).
 
 
+What's new in psycopg 2.5.4
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+- Don't ignore silently the `cursor.callproc` argument without a length.
+
+
 What's new in psycopg 2.5.3
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/psycopg/cursor_type.c b/psycopg/cursor_type.c
index 623ed128..ddbed298 100644
--- a/psycopg/cursor_type.c
+++ b/psycopg/cursor_type.c
@@ -1032,8 +1032,7 @@ psyco_curs_callproc(cursorObject *self, PyObject *args)
     }
 
     if (parameters != Py_None) {
-        nparameters = PyObject_Length(parameters);
-        if (nparameters < 0) nparameters = 0;
+        if (-1 == (nparameters = PyObject_Length(parameters))) { goto exit; }
     }
 
     /* allocate some memory, build the SQL and create a PyString from it */