@@ -143,11 +143,7 @@ typedef struct _cstack {
     PyObject_VAR_HEAD
     struct _cstack *next;
     struct _cstack *prev;
-#ifdef have_long_long
-    long_long serial;
-#else
-    long serial;
-#endif
+    PY_LONG_LONG serial;
     struct _tasklet *task;
     int nesting_level;
     PyThreadState *tstate;
 
@@ -76,13 +76,8 @@ typedef struct _sts {
      * stack belongs.  This is used to find out if a stack switch
      * is required when the main tasklet exits
      */
-#ifdef have_long_long
-    long_long serial;
-    long_long serial_last_jump;
-#else
-    long serial;
-    long serial_last_jump;
-#endif
+    PY_LONG_LONG serial;
+    PY_LONG_LONG serial_last_jump;
     /* the blueprint for new stacks */
     struct _cstack *initial_stub;
     /* the base address for hijacking stacks. XXX deprecating */
 
@@ -9,6 +9,12 @@ What's New in Stackless 3.X.X?
 
 *Release date: 20XX-XX-XX*
 
+- https://github.com/stackless-dev/stackless/issues/221
+  Change the width of C-stack serial numbers to 64bit. This prevents overflows
+  in long running applications with an embedded Stackless Python.
+  This change affects internal Stackless C structures PyStacklessState and
+  PyCStackObject. If you tamper with them, you must recompile your code!
+
 - https://github.com/stackless-dev/stackless/issues/219
   Fix a NULL pointer access in PyStackless_Schedule, if this function is called
   from from "outside" and if no current tasklet exists.
 
@@ -936,7 +936,7 @@ test_outside(PyObject *self)
     int recursion_depth = ts->recursion_depth;
     int nesting_level = ts->st.nesting_level;
     PyObject *ret = Py_None;
-    int jump = ts->st.serial_last_jump;
+    PY_LONG_LONG jump = ts->st.serial_last_jump;
 
     Py_INCREF(ret);
     ts->st.main = NULL;