diff --git a/libraries/common/src/main/java/androidx/media3/common/util/Clock.java b/libraries/common/src/main/java/androidx/media3/common/util/Clock.java
index 668eff9047..a397bead82 100644
--- a/libraries/common/src/main/java/androidx/media3/common/util/Clock.java
+++ b/libraries/common/src/main/java/androidx/media3/common/util/Clock.java
@@ -18,6 +18,7 @@ package androidx.media3.common.util;
 import android.os.Handler;
 import android.os.Looper;
 import androidx.annotation.Nullable;
+import org.checkerframework.checker.initialization.qual.UnknownInitialization;
 
 /**
  * An interface through which system clocks can be read and {@link HandlerWrapper}s created. The
@@ -55,7 +56,8 @@ public interface Clock {
    *
    * @see Handler#Handler(Looper, Handler.Callback)
    */
-  HandlerWrapper createHandler(Looper looper, @Nullable Handler.Callback callback);
+  HandlerWrapper createHandler(
+      Looper looper, @Nullable Handler.@UnknownInitialization Callback callback);
 
   /**
    * Notifies the clock that the current thread is about to be blocked and won't return until a
diff --git a/libraries/common/src/main/java/androidx/media3/common/util/SystemClock.java b/libraries/common/src/main/java/androidx/media3/common/util/SystemClock.java
index 07b009923d..3765f0f5e6 100644
--- a/libraries/common/src/main/java/androidx/media3/common/util/SystemClock.java
+++ b/libraries/common/src/main/java/androidx/media3/common/util/SystemClock.java
@@ -19,6 +19,7 @@ import android.os.Handler;
 import android.os.Handler.Callback;
 import android.os.Looper;
 import androidx.annotation.Nullable;
+import org.checkerframework.checker.initialization.qual.UnknownInitialization;
 
 /**
  * The standard implementation of {@link Clock}, an instance of which is available via {@link
@@ -50,7 +51,9 @@ public class SystemClock implements Clock {
   }
 
   @Override
-  public HandlerWrapper createHandler(Looper looper, @Nullable Callback callback) {
+  @SuppressWarnings({"nullness:argument", "nullness:return"})
+  public HandlerWrapper createHandler(
+      Looper looper, @Nullable @UnknownInitialization Callback callback) {
     return new SystemHandlerWrapper(new Handler(looper, callback));
   }
 
diff --git a/libraries/test_utils/src/main/java/androidx/media3/test/utils/FakeClock.java b/libraries/test_utils/src/main/java/androidx/media3/test/utils/FakeClock.java
index c56fbbedd4..06ba3d15b0 100644
--- a/libraries/test_utils/src/main/java/androidx/media3/test/utils/FakeClock.java
+++ b/libraries/test_utils/src/main/java/androidx/media3/test/utils/FakeClock.java
@@ -35,6 +35,7 @@ import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
+import org.checkerframework.checker.initialization.qual.UnknownInitialization;
 
 /**
  * Fake {@link Clock} implementation that allows to {@link #advanceTime(long) advance the time}
@@ -171,7 +172,9 @@ public class FakeClock implements Clock {
   }
 
   @Override
-  public HandlerWrapper createHandler(Looper looper, @Nullable Callback callback) {
+  @SuppressWarnings({"nullness:argument", "nullness:return"})
+  public HandlerWrapper createHandler(
+      Looper looper, @Nullable @UnknownInitialization Callback callback) {
     return new ClockHandler(looper, callback);
   }