diff --git a/CHANGES.txt b/CHANGES.txt
index 570d7cfdd4..197b627b7c 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -14,6 +14,7 @@ Merged from 4.1:
  * Disk usage guardrail cannot be disabled when failure threshold is reached (CASSANDRA-21057)
  * ReadCommandController should close fast to avoid deadlock when building secondary index (CASSANDRA-19564)
 Merged from 4.0:
+ * Node does not send multiple inflight echos (CASSANDRA-18866)
  * Obsolete expired SSTables before compaction starts (CASSANDRA-19776)
  * Switch lz4-java to at.yawk.lz4 version due to CVE (CASSANDRA-21052)
  * Restrict BytesType compatibility to scalar types only (CASSANDRA-20982)
diff --git a/src/java/org/apache/cassandra/gms/Gossiper.java b/src/java/org/apache/cassandra/gms/Gossiper.java
index 3d4bc95cac..647441ffba 100644
--- a/src/java/org/apache/cassandra/gms/Gossiper.java
+++ b/src/java/org/apache/cassandra/gms/Gossiper.java
@@ -165,6 +165,9 @@ public class Gossiper implements IFailureDetectionEventListener, GossiperMBean,
     @VisibleForTesting
     final Set<InetAddressAndPort> liveEndpoints = new ConcurrentSkipListSet<>();
 
+    /* Inflight echo requests. */
+    private final Map<InetAddressAndPort, EndpointState> inflightEcho = new ConcurrentHashMap<>();
+
     /* unreachable member set */
     private final Map<InetAddressAndPort, Long> unreachableEndpoints = new ConcurrentHashMap<>();
 
@@ -206,6 +209,7 @@ public class Gossiper implements IFailureDetectionEventListener, GossiperMBean,
     {
         unreachableEndpoints.clear();
         liveEndpoints.clear();
+        inflightEcho.clear();
         justRemovedEndpoints.clear();
         expireTimeEndpointMap.clear();
         endpointStateMap.clear();
@@ -725,6 +729,7 @@ public class Gossiper implements IFailureDetectionEventListener, GossiperMBean,
                 logger.warn("Seeds list is now empty!");
         }
 
+        inflightEcho.remove(endpoint);
         if (disableEndpointRemoval)
             return;
 
@@ -1431,14 +1436,24 @@ public class Gossiper implements IFailureDetectionEventListener, GossiperMBean,
     {
         localState.markDead();
 
-        Message<NoPayload> echoMessage = Message.out(ECHO_REQ, noPayload);
-        logger.trace("Sending ECHO_REQ to {}", addr);
-        RequestCallback echoHandler = msg ->
+        EndpointState prevState = inflightEcho.put(addr, localState);
+        boolean sendEcho = !localState.equals(prevState);
+        if (sendEcho)
         {
-            runInGossipStageBlocking(() -> realMarkAlive(addr, localState));
-        };
-
-        MessagingService.instance().sendWithCallback(echoMessage, addr, echoHandler);
+            Message<NoPayload> echoMessage = Message.out(ECHO_REQ, noPayload);
+            logger.trace("Sending ECHO_REQ to {}", addr);
+            RequestCallback echoHandler = msg ->
+            {
+                runInGossipStageBlocking(() -> {
+                    EndpointState epState = inflightEcho.remove(addr);
+                    if (epState != null)
+                        realMarkAlive(addr, epState);
+                });
+            };
+            MessagingService.instance().sendWithCallback(echoMessage, addr, echoHandler);
+        }
+        else
+            logger.trace("Skipping ECHO_REQ to {} since it is already inflight", addr);
 
         GossiperDiagnostics.markedAlive(this, addr, localState);
     }
@@ -1488,6 +1503,7 @@ public class Gossiper implements IFailureDetectionEventListener, GossiperMBean,
     private void silentlyMarkDead(InetAddressAndPort addr, EndpointState localState)
     {
         localState.markDead();
+        inflightEcho.remove(addr);
         if (!disableEndpointRemoval)
         {
             liveEndpoints.remove(addr);