diff --git a/libp2p/src/main/kotlin/io/libp2p/pubsub/AbstractRouter.kt b/libp2p/src/main/kotlin/io/libp2p/pubsub/AbstractRouter.kt
index eb8033ce..4dd76409 100644
--- a/libp2p/src/main/kotlin/io/libp2p/pubsub/AbstractRouter.kt
+++ b/libp2p/src/main/kotlin/io/libp2p/pubsub/AbstractRouter.kt
@@ -323,7 +323,11 @@ abstract class AbstractRouter(
 
     override fun getPeerTopics(): CompletableFuture<Map<PeerId, Set<Topic>>> {
         return submitOnEventThread {
-            peersTopics.asFirstToSecondMap().mapKeys { it.key.peerId }
+            peersTopics.asFirstToSecondMap()
+                .map { (key, value) ->
+                    key.peerId to value.toSet()
+                }
+                .toMap()
         }
     }
 
diff --git a/libp2p/src/test/kotlin/io/libp2p/pubsub/PubsubRouterTest.kt b/libp2p/src/test/kotlin/io/libp2p/pubsub/PubsubRouterTest.kt
index b06f713b..cc45118e 100644
--- a/libp2p/src/test/kotlin/io/libp2p/pubsub/PubsubRouterTest.kt
+++ b/libp2p/src/test/kotlin/io/libp2p/pubsub/PubsubRouterTest.kt
@@ -1,7 +1,13 @@
 package io.libp2p.pubsub
 
-import io.libp2p.core.pubsub.*
+import io.libp2p.core.pubsub.MessageApi
+import io.libp2p.core.pubsub.RESULT_INVALID
+import io.libp2p.core.pubsub.RESULT_VALID
+import io.libp2p.core.pubsub.Subscriber
 import io.libp2p.core.pubsub.Topic
+import io.libp2p.core.pubsub.ValidationResult
+import io.libp2p.core.pubsub.Validator
+import io.libp2p.core.pubsub.createPubsubApi
 import io.libp2p.etc.types.seconds
 import io.libp2p.etc.types.toByteBuf
 import io.libp2p.etc.types.toBytesBigEndian
@@ -10,6 +16,7 @@ import io.libp2p.pubsub.gossip.GossipRouter
 import io.libp2p.tools.TestChannel.TestConnection
 import io.netty.handler.logging.LogLevel
 import io.netty.util.ResourceLeakDetector
+import org.assertj.core.api.Assertions.assertThat
 import org.junit.jupiter.api.Assertions
 import org.junit.jupiter.api.Test
 import pubsub.pb.Rpc
@@ -279,7 +286,10 @@ abstract class PubsubRouterTest(val routerFactory: DeterministicFuzzRouterFactor
         doTenNeighborsTopology()
     }
 
-    fun doTenNeighborsTopology(randomSeed: Int = 0, routerFactory: DeterministicFuzzRouterFactory = this.routerFactory) {
+    fun doTenNeighborsTopology(
+        randomSeed: Int = 0,
+        routerFactory: DeterministicFuzzRouterFactory = this.routerFactory
+    ) {
         val fuzz = DeterministicFuzz().also {
             it.randomSeed = randomSeed.toLong()
         }
@@ -398,6 +408,7 @@ abstract class PubsubRouterTest(val routerFactory: DeterministicFuzzRouterFactor
         routers[1].connectSemiDuplex(routers[2], pubsubLogs = LogLevel.ERROR)
 
         val apis = routers.map { createPubsubApi(it.router) }
+
         class RecordingSubscriber : Subscriber {
             var count = 0
             override fun accept(t: MessageApi) {
@@ -460,4 +471,54 @@ abstract class PubsubRouterTest(val routerFactory: DeterministicFuzzRouterFactor
         Assertions.assertEquals(2, subs2[2].count)
         Assertions.assertEquals(0, subs2[3].count)
     }
+
+    @Test
+    fun `getPeerTopics() should return immutable snapshot`() {
+        val fuzz = DeterministicFuzz()
+
+        fun <T> executeAsyncNow(asyncTask: () -> CompletableFuture<T>): T {
+            val future = asyncTask()
+            fuzz.timeController.addTime(Duration.ofMillis(1))
+            if (!future.isDone) throw AssertionError("Async task was not complete within virtual 1ms")
+            return future.join()
+        }
+
+        val router1 = fuzz.createTestRouter(routerFactory)
+        val router2 = fuzz.createTestRouter(routerFactory)
+        router2.router.subscribe("topic1")
+
+        router1.connectSemiDuplex(router2, LogLevel.DEBUG, LogLevel.DEBUG)
+
+        val peerTopics1 = executeAsyncNow { router1.router.getPeerTopics() }
+        val peerTopics1MapIt = peerTopics1.entries.iterator()
+        val peerTopics1SetIt = peerTopics1.entries.first().value.iterator()
+
+        router2.router.subscribe("topic2")
+
+        val router3 = fuzz.createTestRouter(routerFactory)
+        router3.router.subscribe("topic3")
+        router1.connectSemiDuplex(router3, LogLevel.DEBUG, LogLevel.DEBUG)
+
+        val peerTopics2 = executeAsyncNow { router1.router.getPeerTopics() }
+
+        assertThat(peerTopics2)
+            .containsExactlyInAnyOrderEntriesOf(
+                mapOf(
+                    router2.peerId to setOf("topic1", "topic2"),
+                    router3.peerId to setOf("topic3")
+                )
+            )
+
+        assertThat(peerTopics1)
+            .containsExactlyInAnyOrderEntriesOf(
+                mapOf(
+                    router2.peerId to setOf("topic1")
+                )
+            )
+
+        assertThat(peerTopics1MapIt.next().key).isEqualTo(router2.peerId)
+        assertThat(peerTopics1MapIt.hasNext()).isFalse()
+        assertThat(peerTopics1SetIt.next()).isEqualTo("topic1")
+        assertThat(peerTopics1SetIt.hasNext()).isFalse()
+    }
 }