diff --git a/bitchat/Utils/MessageDeduplicator.swift b/bitchat/Utils/MessageDeduplicator.swift
index 215384fa..27909ad4 100644
--- a/bitchat/Utils/MessageDeduplicator.swift
+++ b/bitchat/Utils/MessageDeduplicator.swift
@@ -61,6 +61,7 @@ final class MessageDeduplicator {
             let now = Date()
             entries.append(Entry(id: id, timestamp: now))
             lookup[id] = now
+            trimIfNeeded()
         }
     }
 
diff --git a/bitchatTests/MessageDeduplicatorTests.swift b/bitchatTests/MessageDeduplicatorTests.swift
new file mode 100644
index 00000000..6016d7a9
--- /dev/null
+++ b/bitchatTests/MessageDeduplicatorTests.swift
@@ -0,0 +1,28 @@
+//
+// MessageDeduplicatorTests.swift
+// bitchatTests
+//
+// Tests for MessageDeduplicator.
+// This is free and unencumbered software released into the public domain.
+//
+
+import Foundation
+import Testing
+@testable import bitchat
+
+@Suite("Message Deduplicator")
+struct MessageDeduplicatorTests {
+    @Test func markProcessed_enforcesMaximumCount() {
+        let deduplicator = MessageDeduplicator(maxAge: 300, maxCount: 4)
+
+        for id in ["a", "b", "c", "d", "e"] {
+            deduplicator.markProcessed(id)
+        }
+
+        #expect(!deduplicator.contains("a"))
+        #expect(!deduplicator.contains("b"))
+        #expect(deduplicator.contains("c"))
+        #expect(deduplicator.contains("d"))
+        #expect(deduplicator.contains("e"))
+    }
+}