diff --git a/src/base/base_math.c b/src/base/base_math.c
index c80a5360..feb962f7 100644
--- a/src/base/base_math.c
+++ b/src/base/base_math.c
@@ -758,6 +758,7 @@ rng1u64_list_concat(Rng1U64List *list, Rng1U64List *to_concat)
       list->first = to_concat->first;
       list->last  = to_concat->last;
     }
+    list->count += to_concat->count;
     MemoryZeroStruct(to_concat);
   }
 }