diff --git a/psycopg/typecast_array.c b/psycopg/typecast_array.c
index b5f1062c..75fa1cfa 100644
--- a/psycopg/typecast_array.c
+++ b/psycopg/typecast_array.c
@@ -224,9 +224,9 @@ typecast_array_scan(const char *str, Py_ssize_t strlength,
         }
 
         else if (state == ASCAN_END) {
-            if (--stack_index < 0)
+            if (stack_index == 0)
                 return -1;
-            array = stack[stack_index];
+            array = stack[--stack_index];
         }
 
         else if (state ==  ASCAN_EOF)