diff --git a/mobile/android/base/preferences/CustomListPreference.java b/mobile/android/base/preferences/CustomListPreference.java
index 502e134c7057..cafb392ffceb 100644
--- a/mobile/android/base/preferences/CustomListPreference.java
+++ b/mobile/android/base/preferences/CustomListPreference.java
@@ -80,8 +80,12 @@ public abstract class CustomListPreference extends Preference implements View.On
     protected abstract int getPreferenceLayoutResource();
 
     /**
-     * Set whether this object's UI should display this as the default item. To ensure proper ordering,
-     * this method should only be called after this Preference is added to the PreferenceCategory.
+     * Set whether this object's UI should display this as the default item.
+     * Note: This must be called from the UI thread because it touches the view hierarchy.
+     *
+     * To ensure proper ordering, this method should only be called after this Preference
+     * is added to the PreferenceCategory.
+     *
      * @param isDefault Flag indicating if this represents the default list item.
      */
     public void setIsDefault(boolean isDefault) {
diff --git a/mobile/android/base/preferences/SearchPreferenceCategory.java b/mobile/android/base/preferences/SearchPreferenceCategory.java
index 121f1283a626..0c2fcb6ccc79 100644
--- a/mobile/android/base/preferences/SearchPreferenceCategory.java
+++ b/mobile/android/base/preferences/SearchPreferenceCategory.java
@@ -16,6 +16,7 @@ import org.json.JSONObject;
 import org.mozilla.gecko.GeckoAppShell;
 import org.mozilla.gecko.GeckoEvent;
 import org.mozilla.gecko.util.GeckoEventListener;
+import org.mozilla.gecko.util.ThreadUtils;
 
 public class SearchPreferenceCategory extends CustomListCategory implements GeckoEventListener {
     public static final String LOGTAG = "SearchPrefCategory";
@@ -81,7 +82,7 @@ public class SearchPreferenceCategory extends CustomListCategory implements Geck
                     JSONObject engineJSON = engines.getJSONObject(i);
                     final String engineName = engineJSON.getString("name");
 
-                    SearchEnginePreference enginePreference = new SearchEnginePreference(getContext(), this);
+                    final SearchEnginePreference enginePreference = new SearchEnginePreference(getContext(), this);
                     enginePreference.setSearchEngineFromJSON(engineJSON);
                     enginePreference.setOnPreferenceClickListener(new OnPreferenceClickListener() {
                         @Override
@@ -100,7 +101,12 @@ public class SearchPreferenceCategory extends CustomListCategory implements Geck
                         // We set this here, not in setSearchEngineFromJSON, because it allows us to
                         // keep a reference  to the default engine to use when the AlertDialog
                         // callbacks are used.
-                        enginePreference.setIsDefault(true);
+                        ThreadUtils.postToUiThread(new Runnable() {
+                            @Override
+                            public void run() {
+                                enginePreference.setIsDefault(true);
+                            }
+                        });
                         mDefaultReference = enginePreference;
                     }
                 } catch (JSONException e) {