diff --git a/js/main-editor.js b/js/main-editor.js
index 7ca3e79..f1f64f5 100644
--- a/js/main-editor.js
+++ b/js/main-editor.js
@@ -2631,7 +2631,7 @@ export class Editor extends PrimaryView {
             }, 60 * 1000);
         });
         _make_button("Share", ev => {
-            let data = util.b64encode(c2g.synthesize_level(this.stored_level));
+            let data = util.b64encode(fflate.zlibSync(new Uint8Array(c2g.synthesize_level(this.stored_level))));
             let url = new URL(location);
             url.searchParams.delete('level');
             url.searchParams.delete('setpath');
diff --git a/js/main.js b/js/main.js
index dee3cb8..17f0c0f 100644
--- a/js/main.js
+++ b/js/main.js
@@ -3263,6 +3263,11 @@ async function main() {
     else if (b64level) {
         // TODO all the more important to show errors!!
         let buf = util.b64decode(b64level);
+        let u8array = new Uint8Array(buf);
+        if (u8array[0] === 0x78) {
+            // zlib compressed
+            buf = fflate.unzlibSync(u8array).buffer;
+        }
         await conductor.parse_and_load_game(buf, null, 'shared.c2m', null, "Shared level");
     }
 }