diff --git a/neo/IO/Caching/FIFOSet.cs b/neo/IO/Caching/FIFOSet.cs
index ab6ff1512c..172abdb7fe 100644
--- a/neo/IO/Caching/FIFOSet.cs
+++ b/neo/IO/Caching/FIFOSet.cs
@@ -43,6 +43,7 @@ public bool Add(T item)
                 if (removeCount == maxCapacity)
                 {
                     _lastEntry = _firstEntry = null;
+                    _count = 0;
                 }
                 else
                 {