diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/ThreadSafety.java b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/ThreadSafety.java
index 7379634fe6d2..693d756accac 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/ThreadSafety.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/ThreadSafety.java
@@ -367,16 +367,12 @@ public static Violation create(ConsPStack<String> path) {
       return new AutoValue_ThreadSafety_Violation(path);
     }
 
-    /**
-     * @return true if a violation was found
-     */
+    /** Returns true if a violation was found. */
     public boolean isPresent() {
       return !path().isEmpty();
     }
 
-    /**
-     * @return the explanation
-     */
+    /** Returns the explanation. */
     public String message() {
       return Joiner.on(", ").join(path());
     }
@@ -658,6 +654,9 @@ public Violation visitType(Type type, Void s) {
         }
         return Violation.absent();
       }
+      if (WellKnownMutability.isProtoEnum(state, type)) {
+        return Violation.absent();
+      }
       return Violation.of(
           String.format(
               "the declaration of type '%s' is not annotated with %s",
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/WellKnownMutability.java b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/WellKnownMutability.java
index 15d135620db3..796758ebce98 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/WellKnownMutability.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/WellKnownMutability.java
@@ -342,6 +342,9 @@ private static ImmutableSet<String> buildMutableClasses(List<String> knownMutabl
   private static final Supplier<Type> PROTOCOL_MESSAGE_TYPE =
       Suppliers.typeFromString("com.google.io.protocol.ProtocolMessage");
 
+  private static final Supplier<Type> PROTOCOL_MESSAGE_ENUM =
+      Suppliers.typeFromString("com.google.protobuf.ProtocolMessageEnum");
+
   private static boolean isAssignableTo(Type type, Supplier<Type> supplier, VisitorState state) {
     Type to = supplier.get(state);
     if (to == null) {
@@ -371,6 +374,11 @@ public static boolean isProto2MutableMessageClass(VisitorState state, Type type)
         && !isAssignableTo(type, PROTOCOL_MESSAGE_TYPE, state);
   }
 
+  public static boolean isProtoEnum(VisitorState state, Type type) {
+    checkNotNull(type);
+    return isAssignableTo(type, PROTOCOL_MESSAGE_ENUM, state);
+  }
+
   /** Returns true if the type is an annotation. */
   public static boolean isAnnotation(VisitorState state, Type type) {
     return isAssignableTo(type, Suppliers.ANNOTATION_TYPE, state);
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/threadsafety/ThreadSafeCheckerTest.java b/core/src/test/java/com/google/errorprone/bugpatterns/threadsafety/ThreadSafeCheckerTest.java
index cd682d46480f..3a186843e69d 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/threadsafety/ThreadSafeCheckerTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/threadsafety/ThreadSafeCheckerTest.java
@@ -1084,4 +1084,21 @@ public void threadSafeRecursiveUpperBound_notThreadsafe() {
             "}")
         .doTest();
   }
+
+  @Test
+  public void protoEnum() {
+    compilationHelper
+        .addSourceLines(
+            "E.java",
+            "import com.google.protobuf.ProtocolMessageEnum;",
+            "abstract class E implements ProtocolMessageEnum {",
+            "}")
+        .addSourceLines(
+            "Test.java",
+            "import com.google.errorprone.annotations.ThreadSafe;",
+            "@ThreadSafe class Test {",
+            "  final E x = null;",
+            "}")
+        .doTest();
+  }
 }