diff --git a/poi-ooxml/src/main/java/org/apache/poi/xdgf/usermodel/section/geometry/RelLineTo.java b/poi-ooxml/src/main/java/org/apache/poi/xdgf/usermodel/section/geometry/RelLineTo.java
index e6a9731b66..2ec8d394a9 100644
--- a/poi-ooxml/src/main/java/org/apache/poi/xdgf/usermodel/section/geometry/RelLineTo.java
+++ b/poi-ooxml/src/main/java/org/apache/poi/xdgf/usermodel/section/geometry/RelLineTo.java
@@ -47,6 +47,10 @@ public class RelLineTo implements GeometryRow {
         for (CellType cell : row.getCellArray()) {
             String cellName = cell.getN();
 
+            if (cellName == null) {
+                throw new IllegalStateException("Cannot create a ReLineTo object without a cell-name indicating 'X' or 'Y' direction");
+            }
+
             if (cellName.equals("X")) {
                 x = XDGFCell.parseDoubleValue(cell);
             } else if (cellName.equals("Y")) {
diff --git a/test-data/diagram/clusterfuzz-testcase-minimized-POIVisioFuzzer-6312416206454784.vsdx b/test-data/diagram/clusterfuzz-testcase-minimized-POIVisioFuzzer-6312416206454784.vsdx
new file mode 100644
index 0000000000..e05ab739fa
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diff --git a/test-data/spreadsheet/stress.xls b/test-data/spreadsheet/stress.xls
index a4ba77404e..9b4388c582 100644
Binary files a/test-data/spreadsheet/stress.xls and b/test-data/spreadsheet/stress.xls differ