diff --git a/library/core/src/main/java/com/google/android/exoplayer2/drm/DefaultDrmSessionManager.java b/library/core/src/main/java/com/google/android/exoplayer2/drm/DefaultDrmSessionManager.java
index be02faeba8..67cb095b8d 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/drm/DefaultDrmSessionManager.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/drm/DefaultDrmSessionManager.java
@@ -36,6 +36,7 @@ import com.google.android.exoplayer2.util.Log;
 import com.google.android.exoplayer2.util.MimeTypes;
 import com.google.android.exoplayer2.util.Util;
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Sets;
 import java.lang.annotation.Documented;
 import java.lang.annotation.Retention;
@@ -632,12 +633,12 @@ public class DefaultDrmSessionManager implements DrmSessionManager {
       // ResourceBusyException is only available at API 19, so on earlier versions we always
       // eagerly release regardless of the underlying error.
       if (!keepaliveSessions.isEmpty()) {
-        // Make a local copy, because sessions are removed from this.timingOutSessions during
+        // Make a local copy, because sessions are removed from this.keepaliveSessions during
         // release (via callback).
-        ImmutableList<DefaultDrmSession> timingOutSessions =
-            ImmutableList.copyOf(this.keepaliveSessions);
-        for (DrmSession timingOutSession : timingOutSessions) {
-          timingOutSession.release(/* eventDispatcher= */ null);
+        ImmutableSet<DefaultDrmSession> keepaliveSessions =
+            ImmutableSet.copyOf(this.keepaliveSessions);
+        for (DrmSession keepaliveSession : keepaliveSessions) {
+          keepaliveSession.release(/* eventDispatcher= */ null);
         }
         // Undo the acquisitions from createAndAcquireSession().
         session.release(eventDispatcher);