diff --git a/core/src/main/java/io/parsingdata/metal/Trampoline.java b/core/src/main/java/io/parsingdata/metal/Trampoline.java
index 7f22daa2..0235a069 100644
--- a/core/src/main/java/io/parsingdata/metal/Trampoline.java
+++ b/core/src/main/java/io/parsingdata/metal/Trampoline.java
@@ -44,10 +44,12 @@ static <T> Trampoline<T> complete(final CompletedTrampoline<T> completedTrampoli
     @FunctionalInterface
     interface CompletedTrampoline<T> extends Trampoline<T> {
 
+        @Override
         default boolean hasNext() {
             return false;
         }
 
+        @Override
         default Trampoline<T> next() {
             throw new UnsupportedOperationException("A CompletedTrampoline does not have a next computation.");
         }
@@ -61,10 +63,12 @@ static <T> Trampoline<T> intermediate(final IntermediateTrampoline<T> intermedia
     @FunctionalInterface
     interface IntermediateTrampoline<T> extends Trampoline<T> {
 
+        @Override
         default T result() {
             throw new UnsupportedOperationException("An IntermediateTrampoline does not have a result.");
         }
 
+        @Override
         default boolean hasNext() {
             return true;
         }
diff --git a/core/src/main/java/io/parsingdata/metal/data/ParseGraph.java b/core/src/main/java/io/parsingdata/metal/data/ParseGraph.java
index 03918a15..5e84474f 100644
--- a/core/src/main/java/io/parsingdata/metal/data/ParseGraph.java
+++ b/core/src/main/java/io/parsingdata/metal/data/ParseGraph.java
@@ -117,13 +117,13 @@ private Trampoline<Optional<ParseValue>> current(final ImmutableList<ParseItem>
         return intermediate(() -> current(items.tail));
     }
 
-    public boolean isGraph() { return true; }
-    public ParseGraph asGraph() { return this; }
-    public Token getDefinition() { return definition; }
+    @Override public boolean isGraph() { return true; }
+    @Override public ParseGraph asGraph() { return this; }
+    @Override public Token getDefinition() { return definition; }
 
     @Override
     public String toString() {
-        if (this == EMPTY) {
+        if (this.equals(EMPTY)) {
             return "pg(EMPTY)";
         }
         if (head == null) {
diff --git a/core/src/main/java/io/parsingdata/metal/data/ParseReference.java b/core/src/main/java/io/parsingdata/metal/data/ParseReference.java
index 1becd77a..d6207dbf 100644
--- a/core/src/main/java/io/parsingdata/metal/data/ParseReference.java
+++ b/core/src/main/java/io/parsingdata/metal/data/ParseReference.java
@@ -43,9 +43,9 @@ public Optional<ParseItem> resolve(final ParseGraph root) {
         return findItemAtOffset(getAllRoots(root, definition), location, source).computeResult();
     }
 
-    public boolean isReference() { return true; }
-    public ParseReference asReference() { return this; }
-    public Token getDefinition() { return definition; }
+    @Override public boolean isReference() { return true; }
+    @Override public ParseReference asReference() { return this; }
+    @Override public Token getDefinition() { return definition; }
 
     @Override
     public String toString() {
diff --git a/core/src/main/java/io/parsingdata/metal/data/ParseValue.java b/core/src/main/java/io/parsingdata/metal/data/ParseValue.java
index e2fb8ef5..0f2ea7a6 100644
--- a/core/src/main/java/io/parsingdata/metal/data/ParseValue.java
+++ b/core/src/main/java/io/parsingdata/metal/data/ParseValue.java
@@ -40,9 +40,9 @@ public boolean matches(final String name) {
         return this.name.equals(name) || this.name.endsWith(Token.SEPARATOR + name);
     }
 
-    public boolean isValue() { return true; }
-    public ParseValue asValue() { return this; }
-    public Token getDefinition() { return definition; }
+    @Override public boolean isValue() { return true; }
+    @Override public ParseValue asValue() { return this; }
+    @Override public Token getDefinition() { return definition; }
 
     @Override
     public String toString() {
diff --git a/core/src/main/java/io/parsingdata/metal/encoding/ByteOrder.java b/core/src/main/java/io/parsingdata/metal/encoding/ByteOrder.java
index 8830c015..7f12f65e 100644
--- a/core/src/main/java/io/parsingdata/metal/encoding/ByteOrder.java
+++ b/core/src/main/java/io/parsingdata/metal/encoding/ByteOrder.java
@@ -18,10 +18,10 @@
 
 public enum ByteOrder {
 
-    BIG_ENDIAN { public byte[] apply(final byte[] bytes) {
+    BIG_ENDIAN { @Override public byte[] apply(final byte[] bytes) {
         return bytes.clone();
     } },
-    LITTLE_ENDIAN { public byte[] apply(final byte[] bytes) {
+    LITTLE_ENDIAN { @Override public byte[] apply(final byte[] bytes) {
         final byte[] output = bytes.clone();
         for (int i = 0; i < bytes.length; i++) {
             output[i] = bytes[(bytes.length-1)-i];
diff --git a/core/src/main/java/io/parsingdata/metal/token/Until.java b/core/src/main/java/io/parsingdata/metal/token/Until.java
index 618e644a..a16eeae1 100644
--- a/core/src/main/java/io/parsingdata/metal/token/Until.java
+++ b/core/src/main/java/io/parsingdata/metal/token/Until.java
@@ -101,8 +101,8 @@ private Trampoline<Optional<ParseState>> handleInterval(final Environment enviro
 
     private Trampoline<Optional<ParseState>> iterate(final Environment environment, final BigInteger currentSize, final BigInteger stepSize, final BigInteger maxSize) {
         if (stepSize.compareTo(ZERO) == 0 ||
-            stepSize.compareTo(ZERO) > 0 && currentSize.compareTo(maxSize) > 0 ||
-            stepSize.compareTo(ZERO) < 0 && currentSize.compareTo(maxSize) < 0) {
+            (stepSize.compareTo(ZERO) > 0 && currentSize.compareTo(maxSize) > 0) ||
+            (stepSize.compareTo(ZERO) < 0 && currentSize.compareTo(maxSize) < 0)) {
             return complete(Util::failure);
         }
         return environment.parseState
diff --git a/core/src/test/java/io/parsingdata/metal/AutoEqualityTest.java b/core/src/test/java/io/parsingdata/metal/AutoEqualityTest.java
index 0192cb88..bec338a8 100644
--- a/core/src/test/java/io/parsingdata/metal/AutoEqualityTest.java
+++ b/core/src/test/java/io/parsingdata/metal/AutoEqualityTest.java
@@ -154,27 +154,31 @@ public class AutoEqualityTest {
     private static final List<Supplier<Object>> BIG_INTEGERS = Arrays.asList(() -> ONE, () -> BigInteger.valueOf(3));
     private static final List<Supplier<Object>> PARSE_STATES = Arrays.asList(() -> createFromByteStream(DUMMY_STREAM), () -> createFromByteStream(DUMMY_STREAM, ONE), () -> new ParseState(GRAPH_WITH_REFERENCE, DUMMY_BYTE_STREAM_SOURCE, TEN));
     private static final List<Supplier<Object>> IMMUTABLE_LISTS = Arrays.asList(ImmutableList::new, () -> ImmutableList.create("TEST"), () -> ImmutableList.create(1), () -> ImmutableList.create(1).add(2));
-    private static final Map<Class, List<Supplier<Object>>> mapping = new HashMap<Class, List<Supplier<Object>>>() {{
-        put(String.class, STRINGS);
-        put(Encoding.class, ENCODINGS);
-        put(Token.class, TOKENS);
-        put(Token[].class, TOKEN_ARRAYS);
-        put(ValueExpression.class, VALUE_EXPRESSIONS);
-        put(Expression.class, EXPRESSIONS);
-        put(Value.class, VALUES);
-        put(BinaryOperator.class, REDUCERS);
-        put(Slice.class, SLICES);
-        put(byte[].class, BYTE_ARRAYS);
-        put(Source.class, SOURCES);
-        put(long.class, LONGS);
-        put(int.class, INTEGERS);
-        put(ParseGraph.class, PARSE_GRAPHS);
-        put(ParseItem.class, PARSE_ITEMS);
-        put(ByteStream.class, BYTE_STREAMS);
-        put(BigInteger.class, BIG_INTEGERS);
-        put(ParseState.class, PARSE_STATES);
-        put(ImmutableList.class, IMMUTABLE_LISTS);
-    }};
+    private static final Map<Class, List<Supplier<Object>>> mapping = buildMap();
+
+    private static Map<Class, List<Supplier<Object>>> buildMap() {
+        final Map<Class, List<Supplier<Object>>> result = new HashMap<>();
+        result.put(String.class, STRINGS);
+        result.put(Encoding.class, ENCODINGS);
+        result.put(Token.class, TOKENS);
+        result.put(Token[].class, TOKEN_ARRAYS);
+        result.put(ValueExpression.class, VALUE_EXPRESSIONS);
+        result.put(Expression.class, EXPRESSIONS);
+        result.put(Value.class, VALUES);
+        result.put(BinaryOperator.class, REDUCERS);
+        result.put(Slice.class, SLICES);
+        result.put(byte[].class, BYTE_ARRAYS);
+        result.put(Source.class, SOURCES);
+        result.put(long.class, LONGS);
+        result.put(int.class, INTEGERS);
+        result.put(ParseGraph.class, PARSE_GRAPHS);
+        result.put(ParseItem.class, PARSE_ITEMS);
+        result.put(ByteStream.class, BYTE_STREAMS);
+        result.put(BigInteger.class, BIG_INTEGERS);
+        result.put(ParseState.class, PARSE_STATES);
+        result.put(ImmutableList.class, IMMUTABLE_LISTS);
+        return result;
+    }
 
     @Parameterized.Parameters(name="{0}")
     public static Collection<Object[]> data() throws IllegalAccessException, InvocationTargetException, InstantiationException {
diff --git a/core/src/test/java/io/parsingdata/metal/data/callback/CallbackTest.java b/core/src/test/java/io/parsingdata/metal/data/callback/CallbackTest.java
index 3a04fa23..1183f870 100644
--- a/core/src/test/java/io/parsingdata/metal/data/callback/CallbackTest.java
+++ b/core/src/test/java/io/parsingdata/metal/data/callback/CallbackTest.java
@@ -242,7 +242,7 @@ void assertAllHandled() {
         }
     }
 
-    private class CountingCallback implements Callback {
+    private static class CountingCallback implements Callback {
         private int successCount = 0;
         private int failureCount = 0;
 
diff --git a/core/src/test/java/io/parsingdata/metal/data/selection/ByTokenTest.java b/core/src/test/java/io/parsingdata/metal/data/selection/ByTokenTest.java
index 6f9936ed..e5764976 100644
--- a/core/src/test/java/io/parsingdata/metal/data/selection/ByTokenTest.java
+++ b/core/src/test/java/io/parsingdata/metal/data/selection/ByTokenTest.java
@@ -301,7 +301,7 @@ public void getAllRootsMultiSub() throws IOException {
         }
     }
 
-    private class CustomToken extends Token {
+    private static class CustomToken extends Token {
 
         public final Token token;
 
diff --git a/formats/src/main/java/io/parsingdata/metal/expression/value/GUID.java b/formats/src/main/java/io/parsingdata/metal/expression/value/GUID.java
index 82508d58..1a5d527c 100644
--- a/formats/src/main/java/io/parsingdata/metal/expression/value/GUID.java
+++ b/formats/src/main/java/io/parsingdata/metal/expression/value/GUID.java
@@ -45,7 +45,7 @@ private GUID() {}
      * @return expression to use as predicate
      */
     public static ValueExpression guid(final String guid) {
-        final String[] parts = checkNotNull(guid, "guid").split("-");
+        final String[] parts = checkNotNull(guid, "guid").split("-", -1);
         if (parts.length != 5) {
             throw new IllegalArgumentException("Invalid GUID string: " + guid);
         }
diff --git a/pom.xml b/pom.xml
index e098bde1..a113971e 100644
--- a/pom.xml
+++ b/pom.xml
@@ -67,6 +67,9 @@
     <source-plugin.version>3.0.1</source-plugin.version>
     <pitest-maven.version>1.2.4</pitest-maven.version>
     <maven-jar-plugin.version>3.0.2</maven-jar-plugin.version>
+    <errorprone.maven.compiler.version>3.3</errorprone.maven.compiler.version>
+    <errorprone.plexus.javac.version>2.8.3</errorprone.plexus.javac.version>
+    <errorprone.core.version>2.3.1</errorprone.core.version>
   </properties>
 
   <profiles>
@@ -98,6 +101,30 @@
 
   <build>
     <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>${errorprone.maven.compiler.version}</version>
+        <configuration>
+          <compilerId>javac-with-errorprone</compilerId>
+          <forceJavacCompilerUse>true</forceJavacCompilerUse>
+          <showWarnings>true</showWarnings>
+        </configuration>
+        <dependencies>
+          <dependency>
+            <groupId>org.codehaus.plexus</groupId>
+            <artifactId>plexus-compiler-javac-errorprone</artifactId>
+            <version>${errorprone.plexus.javac.version}</version>
+          </dependency>
+          <!-- override plexus-compiler-javac-errorprone's dependency on
+               Error Prone with the latest version -->
+          <dependency>
+            <groupId>com.google.errorprone</groupId>
+            <artifactId>error_prone_core</artifactId>
+            <version>${errorprone.core.version}</version>
+          </dependency>
+        </dependencies>
+      </plugin>
       <plugin>
         <groupId>org.sonatype.plugins</groupId>
         <artifactId>nexus-staging-maven-plugin</artifactId>