diff --git a/src/main/java/de/vette/idea/neos/lang/yaml/annotators/PrototypeLineMarkerProvider.java b/src/main/java/de/vette/idea/neos/lang/yaml/annotators/PrototypeLineMarkerProvider.java
index e4bdc48f..fc55e750 100644
--- a/src/main/java/de/vette/idea/neos/lang/yaml/annotators/PrototypeLineMarkerProvider.java
+++ b/src/main/java/de/vette/idea/neos/lang/yaml/annotators/PrototypeLineMarkerProvider.java
@@ -29,6 +29,7 @@
 import org.jetbrains.annotations.Nullable;
 import org.jetbrains.yaml.psi.YAMLDocument;
 import org.jetbrains.yaml.psi.YAMLKeyValue;
+import org.jetbrains.yaml.psi.YAMLMapping;
 
 import java.util.Collection;
 import java.util.List;
@@ -56,7 +57,8 @@ public void collectSlowLineMarkers(@NotNull List<PsiElement> elements, @NotNull
                 continue;
             }
 
-            if (((YAMLKeyValue) el).getParentMapping().getParent() instanceof YAMLDocument) {
+            YAMLMapping parentMapping = ((YAMLKeyValue) el).getParentMapping();
+            if (parentMapping != null && parentMapping.getParent() instanceof YAMLDocument) {
                 String nodeType = ((YAMLKeyValue) el).getKeyText();
                 String[] nodeTypeSplit = nodeType.split(":");