diff --git a/src/main/java/io/vertx/core/http/impl/HttpServerImpl.java b/src/main/java/io/vertx/core/http/impl/HttpServerImpl.java
index 11833b7c8..b5939e018 100644
--- a/src/main/java/io/vertx/core/http/impl/HttpServerImpl.java
+++ b/src/main/java/io/vertx/core/http/impl/HttpServerImpl.java
@@ -12,7 +12,8 @@
 package io.vertx.core.http.impl;
 
 import io.netty.bootstrap.ServerBootstrap;
-import io.netty.channel.*;
+import io.netty.channel.Channel;
+import io.netty.channel.ChannelHandler;
 import io.netty.channel.group.ChannelGroup;
 import io.netty.channel.group.ChannelGroupFuture;
 import io.netty.channel.group.DefaultChannelGroup;
@@ -226,10 +227,11 @@ public class HttpServerImpl implements HttpServer, Closeable, MetricsProvider {
       applicationProtocols =  applicationProtocols.stream().filter(v -> v != HttpVersion.HTTP_2).collect(Collectors.toList());
     }
     sslHelper.setApplicationProtocols(applicationProtocols);
-    synchronized (vertx.sharedHttpServers()) {
+    Map<ServerID, HttpServerImpl> sharedHttpServers = vertx.sharedHttpServers();
+    synchronized (sharedHttpServers) {
       this.actualPort = port; // Will be updated on bind for a wildcard port
       id = new ServerID(port, host);
-      HttpServerImpl shared = vertx.sharedHttpServers().get(id);
+      HttpServerImpl shared = sharedHttpServers.get(id);
       if (shared == null || port == 0) {
         serverChannelGroup = new DefaultChannelGroup("vertx-acceptor-channels", GlobalEventExecutor.INSTANCE);
         ServerBootstrap bootstrap = new ServerBootstrap();
@@ -243,7 +245,9 @@ public class HttpServerImpl implements HttpServer, Closeable, MetricsProvider {
           bindFuture = AsyncResolveConnectHelper.doBind(vertx, address, bootstrap);
           bindFuture.addListener(res -> {
             if (res.failed()) {
-              vertx.sharedHttpServers().remove(id);
+              synchronized (sharedHttpServers) {
+                sharedHttpServers.remove(id);
+              }
             } else {
               Channel serverChannel = res.result();
               if (serverChannel.localAddress() instanceof InetSocketAddress) {
@@ -265,7 +269,7 @@ public class HttpServerImpl implements HttpServer, Closeable, MetricsProvider {
           listening = false;
           return this;
         }
-        vertx.sharedHttpServers().put(id, this);
+        sharedHttpServers.put(id, this);
         actualServer = this;
       } else {
         // Server already exists with that host/port - we will use that
diff --git a/src/main/java/io/vertx/core/net/impl/NetServerImpl.java b/src/main/java/io/vertx/core/net/impl/NetServerImpl.java
index 9a8532ce0..fc60ff163 100644
--- a/src/main/java/io/vertx/core/net/impl/NetServerImpl.java
+++ b/src/main/java/io/vertx/core/net/impl/NetServerImpl.java
@@ -167,11 +167,12 @@ public class NetServerImpl implements Closeable, MetricsProvider, NetServer {
     listenContext = vertx.getOrCreateContext();
     registeredHandler = handler;
 
-    synchronized (vertx.sharedNetServers()) {
+    Map<ServerID, NetServerImpl> sharedNetServers = vertx.sharedNetServers();
+    synchronized (sharedNetServers) {
       this.actualPort = socketAddress.port(); // Will be updated on bind for a wildcard port
       String hostOrPath = socketAddress.host() != null ? socketAddress.host() : socketAddress.path();
       id = new ServerID(actualPort, hostOrPath);
-      NetServerImpl shared = vertx.sharedNetServers().get(id);
+      NetServerImpl shared = sharedNetServers.get(id);
       if (shared == null || actualPort == 0) { // Wildcard port will imply a new actual server each time
         serverChannelGroup = new DefaultChannelGroup("vertx-acceptor-channels", GlobalEventExecutor.INSTANCE);
 
@@ -234,13 +235,17 @@ public class NetServerImpl implements Closeable, MetricsProvider, NetServer {
               }
               NetServerImpl.this.id = new ServerID(NetServerImpl.this.actualPort, id.host);
               serverChannelGroup.add(ch);
-              vertx.sharedNetServers().put(id, NetServerImpl.this);
+              synchronized (sharedNetServers) {
+                sharedNetServers.put(id, NetServerImpl.this);
+              }
               VertxMetrics metrics = vertx.metricsSPI();
               if (metrics != null) {
                 this.metrics = metrics.createNetServerMetrics(options, new SocketAddressImpl(id.port, id.host));
               }
             } else {
-              vertx.sharedNetServers().remove(id);
+              synchronized (sharedNetServers) {
+                sharedNetServers.remove(id);
+              }
             }
           });
 
@@ -256,7 +261,7 @@ public class NetServerImpl implements Closeable, MetricsProvider, NetServer {
           return;
         }
         if (actualPort != 0) {
-          vertx.sharedNetServers().put(id, this);
+          sharedNetServers.put(id, this);
         }
         actualServer = this;
       } else {