diff --git a/constants.gradle b/constants.gradle
index b1c2c636c7..9510b8442e 100644
--- a/constants.gradle
+++ b/constants.gradle
@@ -25,6 +25,7 @@ project.ext {
     autoServiceVersion = '1.0-rc4'
     checkerframeworkVersion = '2.5.0'
     jsr305Version = '3.0.2'
+    kotlinAnnotationsVersion = '1.3.31'
     androidXTestVersion = '1.1.0'
     truthVersion = '0.44'
     modulePrefix = ':'
diff --git a/library/core/build.gradle b/library/core/build.gradle
index fda2f079de..d6aee8a35d 100644
--- a/library/core/build.gradle
+++ b/library/core/build.gradle
@@ -61,8 +61,7 @@ dependencies {
     compileOnly 'com.google.code.findbugs:jsr305:' + jsr305Version
     compileOnly 'org.checkerframework:checker-qual:' + checkerframeworkVersion
     compileOnly 'org.checkerframework:checker-compat-qual:' + checkerframeworkVersion
-    // Uncomment to enable Kotlin non-null strict mode. See [internal: b/138703808].
-    // compileOnly "org.jetbrains.kotlin:kotlin-annotations-jvm:1.1.60"
+    compileOnly 'org.jetbrains.kotlin:kotlin-annotations-jvm:' + kotlinAnnotationsVersion
     androidTestImplementation 'androidx.test:runner:' + androidXTestVersion
     androidTestImplementation 'androidx.test.ext:junit:' + androidXTestVersion
     androidTestImplementation 'com.google.truth:truth:' + truthVersion
diff --git a/library/core/proguard-rules.txt b/library/core/proguard-rules.txt
index 1f7a8d0ee7..ab3cc5fccd 100644
--- a/library/core/proguard-rules.txt
+++ b/library/core/proguard-rules.txt
@@ -58,5 +58,6 @@
   <init>(com.google.android.exoplayer2.upstream.DataSource$Factory);
 }
 
-# Don't warn about checkerframework
+# Don't warn about checkerframework and Kotlin annotations
 -dontwarn org.checkerframework.**
+-dontwarn kotlin.annotations.jvm.**
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/util/NonNullApi.java b/library/core/src/main/java/com/google/android/exoplayer2/util/NonNullApi.java
index bd7a70eba0..7678710f18 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/util/NonNullApi.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/util/NonNullApi.java
@@ -20,8 +20,8 @@ import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import javax.annotation.Nonnull;
 import javax.annotation.meta.TypeQualifierDefault;
-// import kotlin.annotations.jvm.MigrationStatus;
-// import kotlin.annotations.jvm.UnderMigration;
+import kotlin.annotations.jvm.MigrationStatus;
+import kotlin.annotations.jvm.UnderMigration;
 
 /**
  * Annotation to declare all type usages in the annotated instance as {@link Nonnull}, unless
@@ -29,8 +29,6 @@ import javax.annotation.meta.TypeQualifierDefault;
  */
 @Nonnull
 @TypeQualifierDefault(ElementType.TYPE_USE)
-// TODO(internal: b/138703808): Uncomment to ensure Kotlin issues compiler errors when non-null
-// types are used incorrectly.
-// @UnderMigration(status = MigrationStatus.STRICT)
+@UnderMigration(status = MigrationStatus.STRICT)
 @Retention(RetentionPolicy.CLASS)
 public @interface NonNullApi {}