diff --git a/i18n-format.js b/i18n-format.js
index 7be8609..7090e83 100644
--- a/i18n-format.js
+++ b/i18n-format.js
@@ -269,7 +269,10 @@ export class I18nFormat extends polyfill(HTMLElement) {
     return true;
   }
   set observeParams(value) {
-    console.warn(`${this.is}: observeParams is deprecated and has a read-only dummy value true.`);
+    if (!this.constructor._observeParamsWarned) {
+      console.warn(`${this.is}: observeParams is deprecated and has a read-only dummy value true.`);
+      this.constructor._observeParamsWarned = true;
+    }
   }
 
   connectedCallback() {
diff --git a/package.json b/package.json
index eaf1140..852400d 100644
--- a/package.json
+++ b/package.json
@@ -18,7 +18,7 @@
   },
   "homepage": "https://github.com/t2ym/i18n-format#readme",
   "name": "i18n-format",
-  "version": "4.0.0-pre.3",
+  "version": "4.0.0-pre.4",
   "main": "i18n-format.js",
   "directories": {
     "test": "test"
diff --git a/test/basic-test.html b/test/basic-test.html
index cffaeb2..b866c1f 100755
--- a/test/basic-test.html
+++ b/test/basic-test.html
@@ -366,6 +366,8 @@
       assert.equal(el.observeParams, true, 'default observeParams is true');
       el.observeParams = false;
       assert.equal(el.observeParams, true, 'observeParams is always true');
+      el.observeParams = false;
+      assert.equal(el.observeParams, true, 'observeParams is always true');
     });
 
     test('default textContent is empty', function () {