diff --git a/webrtc/src/main/java/dev/onvoid/webrtc/client/Whep.java b/webrtc/src/main/java/dev/onvoid/webrtc/client/Whep.java
index cde25cb0..cf47f0bd 100644
--- a/webrtc/src/main/java/dev/onvoid/webrtc/client/Whep.java
+++ b/webrtc/src/main/java/dev/onvoid/webrtc/client/Whep.java
@@ -170,8 +170,15 @@ public CompletableFuture<Session> play(WebRtc rtc) {
 
 			PeerImpl peer = (PeerImpl) rtc.createPeer(options.build());
 
-			return peer.toPublic(HttpSession.negotiate(rtc, peer, endpoint, bearerToken, timeout)
-					.thenApply(resource -> new Session(rtc, peer, resource, bearerToken, timeout)));
+			try {
+				return peer.toPublic(HttpSession.negotiate(rtc, peer, endpoint, bearerToken, timeout)
+						.thenApply(resource -> new Session(rtc, peer, resource, bearerToken, timeout)));
+			}
+			catch (RuntimeException | Error e) {
+				// Until the session has it, no one else would close the peer.
+				peer.close();
+				throw e;
+			}
 		}
 	}
 }
diff --git a/webrtc/src/main/java/dev/onvoid/webrtc/client/Whip.java b/webrtc/src/main/java/dev/onvoid/webrtc/client/Whip.java
index 044b2b0e..5414858a 100644
--- a/webrtc/src/main/java/dev/onvoid/webrtc/client/Whip.java
+++ b/webrtc/src/main/java/dev/onvoid/webrtc/client/Whip.java
@@ -147,7 +147,9 @@ public Builder timeout(Duration timeout) {
 		 * fails if the endpoint refuses the offer or the peer does not connect
 		 * in time, with nothing left behind on the server.
 		 *
-		 * @throws IllegalStateException if no track was given.
+		 * @throws IllegalStateException    if no track was given.
+		 * @throws IllegalArgumentException if a track was not created by the
+		 *                                  runtime.
 		 */
 		public CompletableFuture<Session> publish(WebRtc rtc) {
 			requireNonNull(rtc, "rtc");
@@ -156,6 +158,13 @@ public CompletableFuture<Session> publish(WebRtc rtc) {
 				throw new IllegalStateException("Give at least one track to publish");
 			}
 
+			// Before the peer exists, so that a wrong track leaves nothing behind.
+			for (LocalTrack track : tracks) {
+				if (!(track instanceof LocalTrackImpl) || ((LocalTrackImpl) track).rtc != rtc) {
+					throw new IllegalArgumentException("The track " + track + " was not created by the runtime");
+				}
+			}
+
 			PeerOptions.Builder options = PeerOptions.builder()
 					.name("whip-" + endpoint.getHost())
 					.negotiation(Negotiation.MANUAL);
@@ -166,12 +175,19 @@ public CompletableFuture<Session> publish(WebRtc rtc) {
 
 			PeerImpl peer = (PeerImpl) rtc.createPeer(options.build());
 
-			for (LocalTrack track : tracks) {
-				peer.addTrack(track);
-			}
+			try {
+				for (LocalTrack track : tracks) {
+					peer.addTrack(track);
+				}
 
-			return peer.toPublic(HttpSession.negotiate(rtc, peer, endpoint, bearerToken, timeout)
-					.thenApply(resource -> new Session(rtc, peer, resource, bearerToken, timeout)));
+				return peer.toPublic(HttpSession.negotiate(rtc, peer, endpoint, bearerToken, timeout)
+						.thenApply(resource -> new Session(rtc, peer, resource, bearerToken, timeout)));
+			}
+			catch (RuntimeException | Error e) {
+				// Until the session has it, no one else would close the peer.
+				peer.close();
+				throw e;
+			}
 		}
 	}
 }
diff --git a/webrtc/src/test/java/dev/onvoid/webrtc/client/HttpSessionTests.java b/webrtc/src/test/java/dev/onvoid/webrtc/client/HttpSessionTests.java
index 924b1d62..a9f3167c 100644
--- a/webrtc/src/test/java/dev/onvoid/webrtc/client/HttpSessionTests.java
+++ b/webrtc/src/test/java/dev/onvoid/webrtc/client/HttpSessionTests.java
@@ -31,6 +31,7 @@
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Executors;
+import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
 import java.util.function.UnaryOperator;
@@ -139,6 +140,48 @@ void refusedOfferLeavesNothing() throws Exception {
 		}
 	}
 
+	@Test
+	void foreignTrackLeavesNothing() throws Exception {
+		WebRtc other = clientRuntime(UnaryOperator.identity());
+
+		try (TestHttpEndpoint endpoint = receivingEndpoint()) {
+			Whip.Builder whip = Whip.to(endpoint.uri()).track(video).track(other.media().customVideo("other"));
+
+			assertThrows(IllegalArgumentException.class, () -> whip.publish(rtc));
+			assertTrue(rtc.peers().isEmpty(), () -> "Peers left: " + rtc.peers());
+			assertTrue(endpoint.requests.isEmpty());
+		}
+		finally {
+			other.close();
+		}
+	}
+
+	@Test
+	void failedStartClosesPeer() throws Exception {
+		// The session's deadline cannot be scheduled, after the peer was created.
+		ManualTimer timer = new ManualTimer();
+		WebRtc client = clientRuntime(builder -> builder.timer(timer));
+
+		try (TestHttpEndpoint endpoint = receivingEndpoint()) {
+			CustomVideo track = client.media().customVideo("video");
+			timer.shutdown();
+
+			assertThrows(RejectedExecutionException.class,
+					() -> Whip.to(endpoint.uri()).track(track).publish(client));
+			assertThrows(RejectedExecutionException.class, () -> Whep.from(endpoint.uri()).play(client));
+
+			for (Peer peer : client.peers()) {
+				PeerImpl impl = (PeerImpl) peer;
+				assertTrue(impl.isClosing(), () -> "Not closing: " + peer);
+				impl.closeInternal().get(TIMEOUT_SECONDS, TimeUnit.SECONDS);
+			}
+			assertTrue(client.peers().isEmpty(), () -> "Peers left: " + client.peers());
+		}
+		finally {
+			client.close();
+		}
+	}
+
 	@Test
 	void lateAnswerDeleted() throws Exception {
 		// The session times out while the offer is out. The server created a