diff --git a/core/java/android/content/res/Resources.java b/core/java/android/content/res/Resources.java
index b559604ea14ec..e525ab3f1f3e5 100644
--- a/core/java/android/content/res/Resources.java
+++ b/core/java/android/content/res/Resources.java
@@ -1760,7 +1760,9 @@ public class Resources {
     public final Theme newTheme() {
         Theme theme = new Theme();
         theme.setImpl(mResourcesImpl.newThemeImpl());
-        mThemeRefs.add(new WeakReference<>(theme));
+        synchronized (mThemeRefs) {
+            mThemeRefs.add(new WeakReference<>(theme));
+        }
         return theme;
     }