diff --git a/src/txmempool.h b/src/txmempool.h
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -625,7 +625,8 @@
      * are in the mapNextTx array). If sanity-checking is turned off, check does
      * nothing.
      */
-    void check(const CCoinsViewCache *pcoins) const;
+    void check(const CCoinsViewCache *pcoins) const
+        EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
     // addUnchecked must updated state for all ancestors of a given transaction,
     // to track size/count of descendant transactions. First version of
diff --git a/src/txmempool.cpp b/src/txmempool.cpp
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -719,6 +719,7 @@
         return;
     }
 
+    AssertLockHeld(::cs_main);
     LOCK(cs);
     LogPrint(BCLog::MEMPOOL,
              "Checking mempool with %u transactions and %u inputs\n",