diff --git a/processor/src/main/java/org/mapstruct/ap/internal/model/Decorator.java b/processor/src/main/java/org/mapstruct/ap/internal/model/Decorator.java
index ab37cb77d..e61a25a47 100644
--- a/processor/src/main/java/org/mapstruct/ap/internal/model/Decorator.java
+++ b/processor/src/main/java/org/mapstruct/ap/internal/model/Decorator.java
@@ -125,7 +125,22 @@ public class Decorator extends GeneratedType {
     @Override
     public SortedSet<Type> getImportTypes() {
         SortedSet<Type> importTypes = super.getImportTypes();
-        addIfImportRequired( importTypes, decoratorType );
+        // DecoratorType needs special handling in case it is nested
+        // calling addIfImportRequired is not the most correct approach since it would
+        // lead to checking if the type is to be imported and that would be false
+        // since the Decorator is a nested class within the Mapper.
+        // However, when generating the Decorator this is not needed,
+        // because the Decorator is a top level class itself
+        // In a nutshell creating the Decorator should have its own ProcessorContext, but it doesn't
+        if ( decoratorType.getPackageName().equalsIgnoreCase( getPackageName() ) ) {
+            if ( decoratorType.getTypeElement() != null &&
+                decoratorType.getTypeElement().getNestingKind().isNested() ) {
+                importTypes.add( decoratorType );
+            }
+        }
+        else {
+            importTypes.add( decoratorType );
+        }
         return importTypes;
     }
 
diff --git a/processor/src/test/java/org/mapstruct/ap/test/bugs/_2021/Issue2021Mapper.java b/processor/src/test/java/org/mapstruct/ap/test/bugs/_2021/Issue2021Mapper.java
new file mode 100644
index 000000000..4627f2232
--- /dev/null
+++ b/processor/src/test/java/org/mapstruct/ap/test/bugs/_2021/Issue2021Mapper.java
@@ -0,0 +1,22 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.ap.test.bugs._2021;
+
+import org.mapstruct.DecoratedWith;
+import org.mapstruct.Mapper;
+
+/**
+ * @author Filip Hrisafov
+ */
+@Mapper
+@DecoratedWith(Issue2021Mapper.Decorator.class)
+public interface Issue2021Mapper {
+
+    abstract class Decorator implements Issue2021Mapper {
+
+    }
+
+}
diff --git a/processor/src/test/java/org/mapstruct/ap/test/bugs/_2021/Issue2021Test.java b/processor/src/test/java/org/mapstruct/ap/test/bugs/_2021/Issue2021Test.java
new file mode 100644
index 000000000..f111799d5
--- /dev/null
+++ b/processor/src/test/java/org/mapstruct/ap/test/bugs/_2021/Issue2021Test.java
@@ -0,0 +1,28 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.ap.test.bugs._2021;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.WithClasses;
+import org.mapstruct.ap.testutil.runner.AnnotationProcessorTestRunner;
+
+/**
+ * @author Filip Hrisafov
+ */
+@IssueKey("2021")
+@RunWith(AnnotationProcessorTestRunner.class)
+@WithClasses({
+    Issue2021Mapper.class
+})
+public class Issue2021Test {
+
+    @Test
+    public void shouldCompile() {
+
+    }
+}