diff --git a/Modules/_stringio.c b/Modules/_stringio.c
index d29fe64..f342048 100644
--- a/Modules/_stringio.c
+++ b/Modules/_stringio.c
@@ -140,6 +140,8 @@
 
     if (PyLong_Check(arg)) {
         size = PyLong_AsSsize_t(arg);
+        if (size == -1 && PyErr_Occurred())
+            return NULL;
     }
     else if (arg == Py_None) {
         /* Read until EOF is reached, by default. */
@@ -179,8 +181,6 @@
         size = PyLong_AsSsize_t(arg);
         if (size == -1 && PyErr_Occurred())
             return NULL;
-        if (size == -1 && PyErr_Occurred())
-            return NULL;
     }
     else if (arg == Py_None) {
         /* Truncate to current position if no argument is passed. */