diff --git a/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/XWPFHeaderFooter.java b/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/XWPFHeaderFooter.java
index 84a02e10f7..225a8f496e 100644
--- a/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/XWPFHeaderFooter.java
+++ b/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/XWPFHeaderFooter.java
@@ -71,11 +71,11 @@ public abstract class XWPFHeaderFooter extends POIXMLDocumentPart implements IBo
      */
     public XWPFHeaderFooter(POIXMLDocumentPart parent, PackagePart part) {
         super(parent, part);
-        this.document = (XWPFDocument) getParent();
-
-        if (this.document == null) {
-            throw new NullPointerException();
+        final POIXMLDocumentPart p = getParent();
+        if (!(p instanceof XWPFDocument)) {
+            throw new IllegalArgumentException("Had unexpected type of parent: " + (p == null ? "<null>" : p.getClass()));
         }
+        this.document = (XWPFDocument) p;
     }
 
     @Override
diff --git a/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/XWPFRelation.java b/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/XWPFRelation.java
index 074a941669..83ed6c11f1 100644
--- a/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/XWPFRelation.java
+++ b/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/XWPFRelation.java
@@ -271,4 +271,12 @@ public final class XWPFRelation extends POIXMLRelation {
         return _table.get(rel);
     }
 
+    @Override
+    public String toString() {
+        return "XWPFRelation{" +
+                //getRelation() + "/" +
+                getContentType() + "/" +
+                getDefaultFileName() +
+                "}";
+    }
 }
diff --git a/test-data/document/clusterfuzz-testcase-minimized-POIXWPFFuzzer-4959857092198400.docx b/test-data/document/clusterfuzz-testcase-minimized-POIXWPFFuzzer-4959857092198400.docx
new file mode 100644
index 0000000000..fc5d388422
Binary files /dev/null and b/test-data/document/clusterfuzz-testcase-minimized-POIXWPFFuzzer-4959857092198400.docx differ
diff --git a/test-data/spreadsheet/stress.xls b/test-data/spreadsheet/stress.xls
index a47f99b2cb..eeecaeb553 100644
Binary files a/test-data/spreadsheet/stress.xls and b/test-data/spreadsheet/stress.xls differ