diff --git a/packages/modern-browsers/TODO.md b/packages/modern-browsers/TODO.md
index 4f51149f8d..cf25a4b75a 100644
--- a/packages/modern-browsers/TODO.md
+++ b/packages/modern-browsers/TODO.md
@@ -25,7 +25,7 @@
 
 - [x] Use `web.browser.legacy` to handle SockJS instead.
 
-- [ ] Load `SockJS` using dynamic `import()` if necessary in modern
+- [x] Load `SockJS` using dynamic `import()` if necessary in modern
       `web.browser` clients.
 
 - [ ] Use different plugins in babel-compiler for `web.browser.legacy`.
diff --git a/packages/socket-stream-client/browser.js b/packages/socket-stream-client/browser.js
index 237a928804..93210be961 100644
--- a/packages/socket-stream-client/browser.js
+++ b/packages/socket-stream-client/browser.js
@@ -184,11 +184,16 @@ export class ClientStream extends StreamClientCommon {
     };
 
     this.socket.onclose = () => {
-      if (this.lastError) {
-        this._lostConnection(this.lastError);
-      } else {
+      Promise.resolve(
+        // If the socket is closing because there was an error, and we
+        // didn't load SockJS before, try loading it dynamically before
+        // retrying the connection.
+        this.lastError &&
+        ! hasSockJS &&
+        import("./sockjs-0.3.4.js")
+      ).done(() => {
         this._lostConnection();
-      }
+      });
     };
 
     this.socket.onerror = error => {
diff --git a/packages/socket-stream-client/package.js b/packages/socket-stream-client/package.js
index fb16c92066..b06f4a81b6 100644
--- a/packages/socket-stream-client/package.js
+++ b/packages/socket-stream-client/package.js
@@ -14,6 +14,7 @@ Package.onUse(function(api) {
   api.use("ecmascript");
   api.use("modern-browsers");
   api.use("retry"); // TODO Try to remove this.
+  api.use("dynamic-import");
 
   api.addFiles("sockjs-0.3.4.js", "web.browser.legacy");
   api.mainModule("browser.js", "client", { lazy: true });