diff --git a/app/src/main/java/net/schueller/peertube/activity/SettingsActivity.java b/app/src/main/java/net/schueller/peertube/activity/SettingsActivity.java
index 33755b3..f4070fd 100644
--- a/app/src/main/java/net/schueller/peertube/activity/SettingsActivity.java
+++ b/app/src/main/java/net/schueller/peertube/activity/SettingsActivity.java
@@ -10,7 +10,10 @@ import android.preference.Preference;
 import android.support.v7.app.ActionBar;
 import android.preference.PreferenceFragment;
 import android.preference.PreferenceManager;
+import android.util.Patterns;
 import android.view.MenuItem;
+import android.widget.Toast;
+
 import net.schueller.peertube.R;
 import java.util.List;
 
@@ -34,6 +37,12 @@ public class SettingsActivity extends AppCompatPreferenceActivity {
     private static Preference.OnPreferenceChangeListener sBindPreferenceSummaryToValueListener = (preference, value) -> {
         String stringValue = value.toString();
 
+        // check URL is valid
+        if (preference.getKey().equals("pref_api_base") && !Patterns.WEB_URL.matcher(stringValue).matches()) {
+            Toast.makeText(preference.getContext(), R.string.invalid_url, Toast.LENGTH_LONG).show();
+            return false;
+        }
+
         preference.setSummary(stringValue);
 
         return true;
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 5ceebec..9a0fbc8 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -59,5 +59,6 @@
     <string name="descr_overflow_button">More</string>
     <string name="menu_share">Share</string>
     <string name="playback_channel_name">PeerTube</string>
+    <string name="invalid_url">Invalid Url!</string>
 
 </resources>