diff --git a/src/txmempool.h b/src/txmempool.h
index ddd87d2eb35..6e286faf805 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -710,9 +710,9 @@ public:
         return mapTx.size();
     }
 
-    uint64_t GetTotalTxSize() const
+    uint64_t GetTotalTxSize() const EXCLUSIVE_LOCKS_REQUIRED(cs)
     {
-        LOCK(cs);
+        AssertLockHeld(cs);
         return totalTxSize;
     }