diff --git a/poi-ooxml/src/main/java/org/apache/poi/ooxml/POIXMLRelation.java b/poi-ooxml/src/main/java/org/apache/poi/ooxml/POIXMLRelation.java
index 5bf576d4e0..e4f6e08ef7 100644
--- a/poi-ooxml/src/main/java/org/apache/poi/ooxml/POIXMLRelation.java
+++ b/poi-ooxml/src/main/java/org/apache/poi/ooxml/POIXMLRelation.java
@@ -205,6 +205,9 @@ public abstract class POIXMLRelation {
             PackageRelationship rel = it.next();
             PackagePartName relName = PackagingURIHelper.createPartName(rel.getTargetURI());
             PackagePart part = corePart.getPackage().getPart(relName);
+            if (part == null) {
+                throw new IllegalArgumentException("Could not read part " + relName + " from " + corePart);
+            }
             return part.getInputStream();
         }
         LOGGER.atWarn().log("No part {} found", getDefaultFileName());
diff --git a/test-data/spreadsheet/clusterfuzz-testcase-minimized-POIXSSFFuzzer-6448258963341312.xlsx b/test-data/spreadsheet/clusterfuzz-testcase-minimized-POIXSSFFuzzer-6448258963341312.xlsx
new file mode 100644
index 0000000000..0707db6706
Binary files /dev/null and b/test-data/spreadsheet/clusterfuzz-testcase-minimized-POIXSSFFuzzer-6448258963341312.xlsx differ
diff --git a/test-data/spreadsheet/stress.xls b/test-data/spreadsheet/stress.xls
index ee43072f5c..a47f99b2cb 100644
Binary files a/test-data/spreadsheet/stress.xls and b/test-data/spreadsheet/stress.xls differ