diff --git a/node-api/src/main/kotlin/net/corda/nodeapi/internal/serialization/AllButBlacklisted.kt b/node-api/src/main/kotlin/net/corda/nodeapi/internal/serialization/AllButBlacklisted.kt
index 03cf25a68f..56c9d5d317 100644
--- a/node-api/src/main/kotlin/net/corda/nodeapi/internal/serialization/AllButBlacklisted.kt
+++ b/node-api/src/main/kotlin/net/corda/nodeapi/internal/serialization/AllButBlacklisted.kt
@@ -40,6 +40,7 @@ object AllButBlacklisted : ClassWhitelist {
             Thread::class.java.name,
             HashSet::class.java.name,
             HashMap::class.java.name,
+            WeakHashMap::class.java.name,
             Dictionary::class.java.name, // Deprecated (marked obsolete) in the jdk
             Hashtable::class.java.name, // see [Dictionary]
             ClassLoader::class.java.name,