diff --git a/poi-ooxml/src/main/java/org/apache/poi/openxml4j/opc/PackagePartName.java b/poi-ooxml/src/main/java/org/apache/poi/openxml4j/opc/PackagePartName.java
index 7883c6d2ae..43853dd3b7 100644
--- a/poi-ooxml/src/main/java/org/apache/poi/openxml4j/opc/PackagePartName.java
+++ b/poi-ooxml/src/main/java/org/apache/poi/openxml4j/opc/PackagePartName.java
@@ -201,7 +201,7 @@ public final class PackagePartName implements Comparable<PackagePartName> {
         }
 
         String uriPath = partURI.getPath();
-        if (uriPath.length() == 0
+        if (uriPath == null || uriPath.isEmpty()
                 || ((uriPath.length() == 1) && (uriPath.charAt(0) == PackagingURIHelper.FORWARD_SLASH_CHAR))) {
             throw new InvalidFormatException(
                     "A part name shall not be empty [M1.1]: "
diff --git a/test-data/spreadsheet/clusterfuzz-testcase-minimized-XLSX2CSVFuzzer-5636439151607808.xlsx b/test-data/spreadsheet/clusterfuzz-testcase-minimized-XLSX2CSVFuzzer-5636439151607808.xlsx
new file mode 100644
index 0000000000..2ab3eeb900
Binary files /dev/null and b/test-data/spreadsheet/clusterfuzz-testcase-minimized-XLSX2CSVFuzzer-5636439151607808.xlsx differ
diff --git a/test-data/spreadsheet/stress.xls b/test-data/spreadsheet/stress.xls
index 34326cd1fc..6b2669be74 100644
Binary files a/test-data/spreadsheet/stress.xls and b/test-data/spreadsheet/stress.xls differ