diff --git a/addons/Dexie.Syncable/package.json b/addons/Dexie.Syncable/package.json
index 63d9b538a..9332ec142 100644
--- a/addons/Dexie.Syncable/package.json
+++ b/addons/Dexie.Syncable/package.json
@@ -55,6 +55,7 @@
       "rollup -c tools/build-configs/rollup.config.js",
       "rollup -c tools/build-configs/rollup.tests.config.js",
       "node tools/replaceVersionAndDate.js dist/dexie-syncable.js",
+      "node tools/replaceVersionAndDate.js test/unit/bundle.js",
       "# eslint ",
       "eslint src --cache"
     ],
diff --git a/addons/Dexie.Syncable/src/Dexie.Syncable.js b/addons/Dexie.Syncable/src/Dexie.Syncable.js
index 9feb4af3c..a7b765c45 100644
--- a/addons/Dexie.Syncable/src/Dexie.Syncable.js
+++ b/addons/Dexie.Syncable/src/Dexie.Syncable.js
@@ -42,7 +42,7 @@ function Syncable (db) {
     if (!db.observable || (db.observable.version !== "{version}" && !/^(3|4)\./.test(db.observable.version)))
         throw new Error(`Missing dexie-observable version 3.x or 4.x`);
     if (db.syncable) {
-        if (db.syncable.version !== "{version}") throw new Error(`Mixed versions of dexie-syncable`);
+        if (db.syncable.version !== "{version}") throw new Error(`Mixed versions of dexie-syncable: "{version}" vs "${db.syncable.version}"`);
         return; // Addon already active.
     }
 
@@ -279,7 +279,7 @@ Syncable.registerSyncProtocol = function(name, protocolInstance) {
 
 if (Dexie.Syncable) {
     if (Dexie.Syncable.version !== "{version}") {
-        throw new Error (`Mixed versions of dexie-syncable`);
+        throw new Error (`Mixed versions of dexie-syncable: "{version}" vs "${Dexie.Syncable.version}"`);
     }
 } else {
     // Register addon in Dexie: