diff --git a/selffuzz/src/test/java/com/code_intelligence/selffuzz/mutation/ArgumentsMutatorFuzzTest.java b/selffuzz/src/test/java/com/code_intelligence/selffuzz/mutation/ArgumentsMutatorFuzzTest.java
index 41164949e..f5d2a6372 100644
--- a/selffuzz/src/test/java/com/code_intelligence/selffuzz/mutation/ArgumentsMutatorFuzzTest.java
+++ b/selffuzz/src/test/java/com/code_intelligence/selffuzz/mutation/ArgumentsMutatorFuzzTest.java
@@ -206,15 +206,13 @@ void fuzz_Enums(MyEnum e0, MyEnum e1, MyEnum e2) {}
 
   @SelfFuzzTest
   void fuzz_ProtoBufs(
-      // com.google.protobuf.StringValue v0, // BUG: makes maxIncreaseSize negative in
-      // LibProtobufMutator.mutate
+      com.google.protobuf.StringValue v0,
       com.google.protobuf.Int32Value v1,
       com.google.protobuf.BoolValue v2,
       com.google.protobuf.UInt64Value v3,
       com.google.protobuf.FloatValue v4,
       com.google.protobuf.DoubleValue v5,
-      // com.google.protobuf.BytesValue v6, // BUG: makes maxIncreaseSize negative in
-      // LibProtobufMutator.mutate
+      com.google.protobuf.BytesValue v6,
       com.google.protobuf.Int64Value v7) {
     if (v7 != null) {
       assertThat(v7.getValue()).isAtLeast(Long.MIN_VALUE);
@@ -224,15 +222,13 @@ void fuzz_ProtoBufs(
 
   @SelfFuzzTest
   void fuzz_ProtoBufsNotNull(
-      // @NotNull com.google.protobuf.StringValue v0, // BUG: makes maxIncreaseSize negative in
-      // LibProtobufMutator.mutate
+      @NotNull com.google.protobuf.StringValue v0,
       @NotNull com.google.protobuf.Int32Value v1,
       @NotNull com.google.protobuf.BoolValue v2,
       @NotNull com.google.protobuf.UInt64Value v3,
       @NotNull com.google.protobuf.FloatValue v4,
       @NotNull com.google.protobuf.DoubleValue v5,
-      // @NotNull com.google.protobuf.BytesValue v6, // BUG: makes maxIncreaseSize negative in
-      // LibProtobufMutator.mutate
+      @NotNull com.google.protobuf.BytesValue v6,
       @NotNull com.google.protobuf.Int64Value v7) {
     if (v7 != null) {
       assertThat(v7.getValue()).isAtLeast(Long.MIN_VALUE);
@@ -240,9 +236,8 @@ void fuzz_ProtoBufsNotNull(
     }
   }
 
-  // BUG: makes maxIncreaseSize negative in LibProtobufMutator.mutate
-  // @SelfFuzzTest
-  // public static void fuzz_TestProtobuf(TestProtobuf o1) {}
+  @SelfFuzzTest
+  public static void fuzz_TestProtobuf(Proto2.TestProtobuf o1) {}
 
   @SelfFuzzTest
   void fuzz_MapField3(Proto3.MapField3 o1) {}
diff --git a/selffuzz/src/test/java/com/code_intelligence/selffuzz/mutation/BUILD.bazel b/selffuzz/src/test/java/com/code_intelligence/selffuzz/mutation/BUILD.bazel
index 208dbca40..298a4026e 100644
--- a/selffuzz/src/test/java/com/code_intelligence/selffuzz/mutation/BUILD.bazel
+++ b/selffuzz/src/test/java/com/code_intelligence/selffuzz/mutation/BUILD.bazel
@@ -10,7 +10,7 @@ java_fuzz_target_test(
     ],
     data = ["//selffuzz/src/test/resources:ArgumentsMutatorFuzzTest-corpus"],
     env = {
-        "_JAVA_OPTIONS": "-Xmx1024m",
+        "_JAVA_OPTIONS": "-Xmx2048m",
     },
     fuzzer_args = [
         # Make sure that the fuzzer can run. Longer fuzzing runs will be done in a separate GH action.
diff --git a/src/main/java/com/code_intelligence/jazzer/mutation/mutator/libfuzzer/LibFuzzerMutatorFactory.java b/src/main/java/com/code_intelligence/jazzer/mutation/mutator/libfuzzer/LibFuzzerMutatorFactory.java
index d2cc897e0..9b9e323f9 100644
--- a/src/main/java/com/code_intelligence/jazzer/mutation/mutator/libfuzzer/LibFuzzerMutatorFactory.java
+++ b/src/main/java/com/code_intelligence/jazzer/mutation/mutator/libfuzzer/LibFuzzerMutatorFactory.java
@@ -113,6 +113,9 @@ private int maxInitialSize() {
 
     @Override
     public byte[] mutate(byte[] value, PseudoRandom prng) {
+      // Enforce length constraints on the input to mutate. We do this because some mutators (e.g.
+      // protobuf mutator) don't enforce length constraints in the read methods.
+      value = enforceLength(value);
       int maxLengthIncrease = maxLength - value.length;
       byte[] mutated = LibFuzzerMutate.mutateDefault(value, maxLengthIncrease);
       return enforceLength(mutated);
diff --git a/src/test/java/com/code_intelligence/jazzer/mutation/mutator/lang/StringMutatorTest.java b/src/test/java/com/code_intelligence/jazzer/mutation/mutator/lang/StringMutatorTest.java
index b4e4fba8c..ef4f2bd1b 100644
--- a/src/test/java/com/code_intelligence/jazzer/mutation/mutator/lang/StringMutatorTest.java
+++ b/src/test/java/com/code_intelligence/jazzer/mutation/mutator/lang/StringMutatorTest.java
@@ -226,6 +226,20 @@ void testReadInputsLongerThanMaxLength() throws IOException {
     assertThat(s).isEqualTo("fooba");
   }
 
+  @Test
+  void testMutateWithInputLongerThanMaxLength() {
+    SerializingMutator<String> mutator =
+        (SerializingMutator<String>)
+            factory.createOrThrow(
+                new TypeHolder<@NotNull @WithUtf8Length(max = 5) String>() {}.annotatedType());
+    assertThat(mutator.toString()).isEqualTo("String");
+    String s = "foobarbazf";
+    try (MockPseudoRandom prng = mockPseudoRandom()) {
+      s = mutator.mutate(s, prng);
+    }
+    assertThat(s.length()).isAtMost(5);
+  }
+
   @Test
   void testMaxLengthMutate() {
     SerializingMutator<String> mutator =