diff --git a/Modules/cStringIO.c b/Modules/cStringIO.c
index 7e75879..b7333fd 100644
--- a/Modules/cStringIO.c
+++ b/Modules/cStringIO.c
@@ -289,6 +289,7 @@
         if (pos < 0) pos = self->pos;
 
         if (self->string_size > pos) self->string_size = pos;
+        self->pos = self->string_size;
 
         Py_INCREF(Py_None);
         return Py_None;