diff --git a/poi-ooxml/src/main/java/org/apache/poi/xslf/usermodel/XSLFDiagram.java b/poi-ooxml/src/main/java/org/apache/poi/xslf/usermodel/XSLFDiagram.java
index 895745711c..5b456538c5 100644
--- a/poi-ooxml/src/main/java/org/apache/poi/xslf/usermodel/XSLFDiagram.java
+++ b/poi-ooxml/src/main/java/org/apache/poi/xslf/usermodel/XSLFDiagram.java
@@ -148,8 +148,12 @@ public class XSLFDiagram extends XSLFGraphicFrame {
         shapeCt.setSpPr(msShapeCt.getSpPr());
 
         CTShapeNonVisual nonVisualCt = shapeCt.addNewNvSpPr();
-        nonVisualCt.setCNvPr(msShapeCt.getNvSpPr().getCNvPr());
-        nonVisualCt.setCNvSpPr(msShapeCt.getNvSpPr().getCNvSpPr());
+        com.microsoft.schemas.office.drawing.x2008.diagram.CTShapeNonVisual nvSpPr = msShapeCt.getNvSpPr();
+        if (nvSpPr == null) {
+            nvSpPr = msShapeCt.addNewNvSpPr();
+        }
+        nonVisualCt.setCNvPr(nvSpPr.getCNvPr());
+        nonVisualCt.setCNvSpPr(nvSpPr.getCNvSpPr());
         nonVisualCt.setNvPr(CTApplicationNonVisualDrawingProps.Factory.newInstance());
         shapeCt.setNvSpPr(nonVisualCt);
 
diff --git a/test-data/slideshow/clusterfuzz-testcase-minimized-POIXSLFFuzzer-6435650376957952.pptx b/test-data/slideshow/clusterfuzz-testcase-minimized-POIXSLFFuzzer-6435650376957952.pptx
new file mode 100644
index 0000000000..8da1ed93f9
Binary files /dev/null and b/test-data/slideshow/clusterfuzz-testcase-minimized-POIXSLFFuzzer-6435650376957952.pptx differ
diff --git a/test-data/spreadsheet/stress.xls b/test-data/spreadsheet/stress.xls
index aec4cdf62e..db5b3318d1 100644
Binary files a/test-data/spreadsheet/stress.xls and b/test-data/spreadsheet/stress.xls differ