diff --git a/CHANGELOG.md b/CHANGELOG.md
index d5d1652573..68ac4ae42e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@
 - Added `Environment` to the `Scope`, allowing you to overwrite the `Environment` set on the options ([#5772](https://github.com/getsentry/sentry-java/pull/5772))
   - The scope `Environment` is also applied to the trace envelope header (DSC), logs, metrics and profiles, so all telemetry of a trace reports the same environment
 
+### Improvements
+
+- Speed up Session Replay and screenshot masking for large `maskViewClasses`/`unmaskViewClasses` lists by using constant-time class lookups ([#6410](https://github.com/getsentry/sentry-java/pull/6410))
+
 ### Fixes
 
 - Keep UI profiling running when `startProfiler` is called before a requested stop takes effect at the end of the current chunk ([#6291](https://github.com/getsentry/sentry-java/pull/6291))
diff --git a/sentry-android-replay/src/test/java/io/sentry/android/replay/capture/SessionCaptureStrategyTest.kt b/sentry-android-replay/src/test/java/io/sentry/android/replay/capture/SessionCaptureStrategyTest.kt
index 281eb1da3b..4c31090cee 100644
--- a/sentry-android-replay/src/test/java/io/sentry/android/replay/capture/SessionCaptureStrategyTest.kt
+++ b/sentry-android-replay/src/test/java/io/sentry/android/replay/capture/SessionCaptureStrategyTest.kt
@@ -46,7 +46,6 @@ import java.util.concurrent.ScheduledExecutorService
 import java.util.concurrent.TimeUnit.MILLISECONDS
 import java.util.concurrent.TimeUnit.SECONDS
 import kotlin.test.Test
-import kotlin.test.assertContentEquals
 import kotlin.test.assertEquals
 import kotlin.test.assertFalse
 import kotlin.test.assertNull
@@ -696,8 +695,8 @@ class SessionCaptureStrategyTest {
           assertEquals(true, optionsEvent[0].optionsPayload["maskAllText"])
           assertEquals(false, optionsEvent[0].optionsPayload["maskAllImages"])
           assertEquals("high", optionsEvent[0].optionsPayload["quality"])
-          assertContentEquals(
-            listOf(
+          assertThat(optionsEvent[0].optionsPayload["maskedViewClasses"] as Collection<*>)
+            .containsExactly(
               "android.widget.TextView",
               "android.webkit.WebView",
               "android.widget.VideoView",
@@ -706,13 +705,9 @@ class SessionCaptureStrategyTest {
               "com.google.android.exoplayer2.ui.PlayerView",
               "com.google.android.exoplayer2.ui.StyledPlayerView",
               "my.custom.View",
-            ),
-            optionsEvent[0].optionsPayload["maskedViewClasses"] as Collection<*>,
-          )
-          assertContentEquals(
-            listOf("android.widget.ImageView"),
-            optionsEvent[0].optionsPayload["unmaskedViewClasses"] as Collection<*>,
-          )
+            )
+          assertThat(optionsEvent[0].optionsPayload["unmaskedViewClasses"] as Collection<*>)
+            .containsExactly("android.widget.ImageView")
         },
       )
   }
diff --git a/sentry/src/main/java/io/sentry/SentryMaskingOptions.java b/sentry/src/main/java/io/sentry/SentryMaskingOptions.java
index dd7c5f9a30..44edff39a3 100644
--- a/sentry/src/main/java/io/sentry/SentryMaskingOptions.java
+++ b/sentry/src/main/java/io/sentry/SentryMaskingOptions.java
@@ -1,7 +1,8 @@
 package io.sentry;
 
+import java.util.Collections;
 import java.util.Set;
-import java.util.concurrent.CopyOnWriteArraySet;
+import java.util.concurrent.ConcurrentHashMap;
 import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -32,7 +33,7 @@ public abstract class SentryMaskingOptions {
    *
    * <p>Default is empty.
    */
-  protected Set<String> maskViewClasses = new CopyOnWriteArraySet<>();
+  protected Set<String> maskViewClasses = Collections.newSetFromMap(new ConcurrentHashMap<>());
 
   /**
    * Ignore all views with the specified class names from masking. The class name is the fully
@@ -44,7 +45,7 @@ public abstract class SentryMaskingOptions {
    *
    * <p>Default is empty.
    */
-  protected Set<String> unmaskViewClasses = new CopyOnWriteArraySet<>();
+  protected Set<String> unmaskViewClasses = Collections.newSetFromMap(new ConcurrentHashMap<>());
 
   /** The class name of the view container that masks all of its children. */
   protected @Nullable String maskViewContainerClass = null;
@@ -92,6 +93,10 @@ public Set<String> getMaskViewClasses() {
   }
 
   public void addMaskViewClass(final @NotNull String className) {
+    // Hybrid SDKs may pass null despite the annotation, and the backing set rejects null keys
+    if (className == null) {
+      return;
+    }
     this.maskViewClasses.add(className);
     this.unmaskViewClasses.remove(className);
   }
@@ -102,6 +107,10 @@ public Set<String> getUnmaskViewClasses() {
   }
 
   public void addUnmaskViewClass(final @NotNull String className) {
+    // Hybrid SDKs may pass null despite the annotation, and the backing set rejects null keys
+    if (className == null) {
+      return;
+    }
     this.unmaskViewClasses.add(className);
     this.maskViewClasses.remove(className);
   }
diff --git a/sentry/src/test/java/io/sentry/SentryMaskingOptionsTest.kt b/sentry/src/test/java/io/sentry/SentryMaskingOptionsTest.kt
index 9f661710dc..3f2a62361e 100644
--- a/sentry/src/test/java/io/sentry/SentryMaskingOptionsTest.kt
+++ b/sentry/src/test/java/io/sentry/SentryMaskingOptionsTest.kt
@@ -40,6 +40,26 @@ class SentryMaskingOptionsTest {
     assertTrue(options.unmaskViewClasses.contains("com.example.MyView"))
   }
 
+  @Test
+  fun `addMaskViewClass ignores null`() {
+    val options = TestMaskingOptions()
+    SentryMaskingOptions::class
+      .java
+      .getMethod("addMaskViewClass", String::class.java)
+      .invoke(options, null)
+    assertTrue(options.maskViewClasses.isEmpty())
+  }
+
+  @Test
+  fun `addUnmaskViewClass ignores null`() {
+    val options = TestMaskingOptions()
+    SentryMaskingOptions::class
+      .java
+      .getMethod("addUnmaskViewClass", String::class.java)
+      .invoke(options, null)
+    assertTrue(options.unmaskViewClasses.isEmpty())
+  }
+
   @Test
   fun `setMaskAllText true adds TextView to maskViewClasses`() {
     val options = TestMaskingOptions()