diff --git a/res/values-ru/text_strings.xml b/res/values-ru/text_strings.xml
index cca04326..3ba9a5ba 100644
--- a/res/values-ru/text_strings.xml
+++ b/res/values-ru/text_strings.xml
@@ -165,9 +165,9 @@
 
 	<string name="c_warning">Внимание</string>
 	<string name="c_error">Ошибка</string>
-	<string name="c_billing_error">Биллинг не поддерживается!</string>
+	<string name="c_billing_error">Биллинг не поддерживается: вы должны иметь Google Checkout аккаунт привязанный в вашему Google аккаунту и должны быть подключены к интернету.</string>
 
-	<string name="c_calc_ad_free_title">Избавиться от рекламы и поддержать проект</string>
+	<string name="c_calc_ad_free_title">Избавиться от рекламы!</string>
 	<string name="c_calc_ad_free_summary">Скидка 50% для первых 100 покупателей</string>
 
 </resources>
\ No newline at end of file
diff --git a/res/values/text_strings.xml b/res/values/text_strings.xml
index f544ea82..88bd117a 100644
--- a/res/values/text_strings.xml
+++ b/res/values/text_strings.xml
@@ -165,9 +165,9 @@
 
 	<string name="c_warning">Warning</string>
 	<string name="c_error">Error</string>
-	<string name="c_billing_error">Billing is not supported!</string>
+	<string name="c_billing_error">Billing is not supported: you must have Google Checkout account linked to your Google account and must be connected to the internet.</string>
 
-	<string name="c_calc_ad_free_title">Get rid of ads and support the project</string>
+	<string name="c_calc_ad_free_title">Get rid of ads!</string>
 	<string name="c_calc_ad_free_summary">50% offer for first 100 customers</string>
 
 </resources>
\ No newline at end of file
diff --git a/src/main/java/org/solovyev/android/calculator/CalculatorPreferencesActivity.java b/src/main/java/org/solovyev/android/calculator/CalculatorPreferencesActivity.java
index d697c36a..90349308 100644
--- a/src/main/java/org/solovyev/android/calculator/CalculatorPreferencesActivity.java
+++ b/src/main/java/org/solovyev/android/calculator/CalculatorPreferencesActivity.java
@@ -29,23 +29,27 @@ public class CalculatorPreferencesActivity extends PreferenceActivity implements
 
 		final Preference addFreePreference = findPreference(CalculatorApplication.AD_FREE_P_KEY);
 
-		addFreePreference.setOnPreferenceClickListener(new Preference.OnPreferenceClickListener() {
-			public boolean onPreferenceClick(Preference preference) {
+		if (!CalculatorApplication.isAdFree(this)) {
+			addFreePreference.setOnPreferenceClickListener(new Preference.OnPreferenceClickListener() {
+				public boolean onPreferenceClick(Preference preference) {
 
-				// check billing availability
-				if (BillingController.checkBillingSupported(CalculatorPreferencesActivity.this) != BillingController.BillingStatus.SUPPORTED) {
-					// warn about not supported billing
-					new AlertDialog.Builder(CalculatorPreferencesActivity.this).setTitle(R.string.c_error).setMessage(R.string.c_billing_error).create().show();
-				} else {
-					if (!CalculatorApplication.isAdFree(CalculatorPreferencesActivity.this)) {
-						// not purchased => show purchase window for user
-						BillingController.requestPurchase(CalculatorPreferencesActivity.this, CalculatorApplication.AD_FREE_PRODUCT_ID, true);
+					// check billing availability
+					if (BillingController.checkBillingSupported(CalculatorPreferencesActivity.this) != BillingController.BillingStatus.SUPPORTED) {
+						// warn about not supported billing
+						new AlertDialog.Builder(CalculatorPreferencesActivity.this).setTitle(R.string.c_error).setMessage(R.string.c_billing_error).create().show();
+					} else {
+						if (!CalculatorApplication.isAdFree(CalculatorPreferencesActivity.this)) {
+							// not purchased => show purchase window for user
+							BillingController.requestPurchase(CalculatorPreferencesActivity.this, CalculatorApplication.AD_FREE_PRODUCT_ID, true);
+						}
 					}
-				}
 
-				return true;
-			}
-		});
+					return true;
+				}
+			});
+		} else {
+			addFreePreference.setEnabled(false);
+		}
 
 		final SharedPreferences preferences = getPreferenceManager().getSharedPreferences();
 		preferences.registerOnSharedPreferenceChangeListener(this);