diff --git a/src/main/java/de/thetaphi/forbiddenapis/gradle/CheckForbiddenApis.java b/src/main/java/de/thetaphi/forbiddenapis/gradle/CheckForbiddenApis.java
index 85c99c10..5fac7cca 100644
--- a/src/main/java/de/thetaphi/forbiddenapis/gradle/CheckForbiddenApis.java
+++ b/src/main/java/de/thetaphi/forbiddenapis/gradle/CheckForbiddenApis.java
@@ -42,6 +42,7 @@
 import org.gradle.api.tasks.Classpath;
 import org.gradle.api.tasks.Input;
 import org.gradle.api.tasks.InputFiles;
+import org.gradle.api.tasks.Internal;
 import org.gradle.api.tasks.Optional;
 import org.gradle.api.tasks.OutputDirectories;
 import org.gradle.api.tasks.ParallelizableTask;
@@ -122,8 +123,8 @@ public class CheckForbiddenApis extends DefaultTask implements PatternFilterable
    * Directories with the class files to check.
    * Defaults to current sourseSet's output directory (Gradle 2/3) or output directories (Gradle 4.0+).
    */
-  @OutputDirectories
   // no @InputDirectories, we use separate getter for a list of all input files
+  @Internal
   public FileCollection getClassesDirs() {
     return classesDirs;
   }
@@ -142,6 +143,7 @@ public void setClassesDirs(FileCollection classesDirs) {
    *  throw an exception!
    */
   @Deprecated
+  @Internal
   public File getClassesDir() {
     final FileCollection col = getClassesDirs();
     return (col == null) ? null : col.getSingleFile();
@@ -160,6 +162,7 @@ public void setClassesDir(File classesDir) {
   }
 
   /** Returns the pattern set to match against class files in {@link #getClassesDir()}. */
+  @Internal
   public PatternSet getPatternSet() {
     return patternSet;
   }
@@ -406,7 +409,7 @@ public void setTargetCompatibility(String targetCompatibility) {
    * The default is a single include with pattern '**/*.class'
    */
   @Override
-  @Input
+  @Internal
   public Set<String> getIncludes() {
     return getPatternSet().getIncludes();
   }
@@ -423,7 +426,7 @@ public CheckForbiddenApis setIncludes(Iterable<String> includes) {
    * Set of patterns matching class files to be excluded from checking.
    */
   @Override
-  @Input
+  @Internal
   public Set<String> getExcludes() {
     return getPatternSet().getExcludes();
   }