diff --git a/src/main/java/com/code_intelligence/jazzer/mutation/mutator/libfuzzer/LibFuzzerMutate.java b/src/main/java/com/code_intelligence/jazzer/mutation/mutator/libfuzzer/LibFuzzerMutate.java
index d32a4a5f4..230ad82e9 100644
--- a/src/main/java/com/code_intelligence/jazzer/mutation/mutator/libfuzzer/LibFuzzerMutate.java
+++ b/src/main/java/com/code_intelligence/jazzer/mutation/mutator/libfuzzer/LibFuzzerMutate.java
@@ -33,6 +33,7 @@ public final class LibFuzzerMutate {
   public static final String MOCK_SIZE_KEY = "libfuzzermutator.mock.newsize";
 
   public static byte[] mutateDefault(byte[] data, int maxSizeIncrease) {
+    require(maxSizeIncrease >= 0);
     byte[] mutatedBytes;
     if (maxSizeIncrease == 0) {
       mutatedBytes = data;
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 79e0632c7..d2cc897e0 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
@@ -71,7 +71,7 @@ public byte[] read(DataInputStream in) throws IOException {
 
     @Override
     public byte[] readExclusive(InputStream in) throws IOException {
-      return readAllBytes(in);
+      return enforceLength(readAllBytes(in));
     }
 
     @Override
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 4da06e7fe..b4e4fba8c 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
@@ -34,6 +34,8 @@
 import com.code_intelligence.jazzer.mutation.support.TestSupport.MockPseudoRandom;
 import com.code_intelligence.jazzer.mutation.support.TypeHolder;
 import com.google.protobuf.ByteString;
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.SplittableRandom;
@@ -211,6 +213,19 @@ void testMinLengthMutate() {
     assertThat(s).isEqualTo("gqrff\0\0\0\0\0");
   }
 
+  @Test
+  void testReadInputsLongerThanMaxLength() throws IOException {
+    SerializingMutator<String> mutator =
+        (SerializingMutator<String>)
+            factory.createOrThrow(
+                new TypeHolder<@NotNull @WithUtf8Length(max = 5) String>() {}.annotatedType());
+    assertThat(mutator.toString()).isEqualTo("String");
+
+    ByteArrayInputStream in = new java.io.ByteArrayInputStream("foobarbazf".getBytes());
+    String s = mutator.readExclusive(in);
+    assertThat(s).isEqualTo("fooba");
+  }
+
   @Test
   void testMaxLengthMutate() {
     SerializingMutator<String> mutator =