diff --git a/doc/Container.ods b/doc/Container.ods
index 6b43ad76..0951ce97 100644
Binary files a/doc/Container.ods and b/doc/Container.ods differ
diff --git a/m-array.h b/m-array.h
index 99141d41..33232d3f 100644
--- a/m-array.h
+++ b/m-array.h
@@ -460,6 +460,7 @@
   {                                                                     \
     ARRAYI_CONTRACT(v);                                                 \
     assert (v->size > 0 && v->ptr != NULL);                             \
+    assert (i < v->size);                                               \
     if (dest)                                                           \
       M_DO_MOVE (oplist, *dest, v->ptr[i]);                             \
     else                                                                \