diff --git a/src/chain.h b/src/chain.h
index 2eb780d499..c2a9cba1e6 100644
--- a/src/chain.h
+++ b/src/chain.h
@@ -328,8 +328,9 @@ public:
 
     //! Raise the validity level of this block index entry.
     //! Returns true if the validity was changed.
-    bool RaiseValidity(enum BlockStatus nUpTo)
+    bool RaiseValidity(enum BlockStatus nUpTo) EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
     {
+        AssertLockHeld(::cs_main);
         assert(!(nUpTo & ~BLOCK_VALID_MASK)); // Only validity flags allowed.
         if (nStatus & BLOCK_FAILED_MASK) return false;
 
diff --git a/src/test/fuzz/chain.cpp b/src/test/fuzz/chain.cpp
index 4f97e1ebb1..8c0ed32d51 100644
--- a/src/test/fuzz/chain.cpp
+++ b/src/test/fuzz/chain.cpp
@@ -58,7 +58,7 @@ FUZZ_TARGET(chain)
         if (block_status & ~BLOCK_VALID_MASK) {
             continue;
         }
-        (void)disk_block_index->RaiseValidity(block_status);
+        WITH_LOCK(::cs_main, (void)disk_block_index->RaiseValidity(block_status));
     }
 
     CBlockIndex block_index{block_header};