diff --git a/src/cpp/ripple/LedgerAcquire.cpp b/src/cpp/ripple/LedgerAcquire.cpp
index 025046b917..1cd2ef1c48 100644
--- a/src/cpp/ripple/LedgerAcquire.cpp
+++ b/src/cpp/ripple/LedgerAcquire.cpp
@@ -528,6 +528,8 @@ int PeerSet::getPeerCount() const
 void LedgerAcquire::filterNodes(std::vector<SHAMapNode>& nodeIDs, std::vector<uint256>& nodeHashes,
 	std::set<SHAMapNode>& recentNodes, int max, bool aggressive)
 { // ask for new nodes in preference to ones we've already asked for
+	assert(nodeIDs.size() == nodeHashes.size());
+
 	std::vector<bool> duplicates;
 	duplicates.reserve(nodeIDs.size());