diff --git a/src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFSheet.java b/src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFSheet.java
index 155aa70556..7eb2a45b39 100644
--- a/src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFSheet.java
+++ b/src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFSheet.java
@@ -379,12 +379,19 @@ public class XSSFSheet extends POIXMLDocumentPart implements Sheet  {
         CTMergeCells ctMergeCells = worksheet.isSetMergeCells() ? worksheet.getMergeCells() : worksheet.addNewMergeCells();
         CTMergeCell ctMergeCell = ctMergeCells.addNewMergeCell();
         ctMergeCell.setRef(region.formatAsString());
-        final int numMergeRegions=ctMergeCells.sizeOfMergeCellArray();
+
+        long count = ctMergeCells.getCount();
+
+        if (count == 0) {
+            count=ctMergeCells.sizeOfMergeCellArray();
+        } else {
+            count++;
+        }
 
         // also adjust the number of merged regions overall
-        ctMergeCells.setCount(numMergeRegions);
+        ctMergeCells.setCount(count);
 
-        return numMergeRegions-1;
+        return Math.toIntExact(count-1);
     }
 
     /**
diff --git a/src/ooxml/testcases/org/apache/poi/xssf/usermodel/TestXSSFBugs.java b/src/ooxml/testcases/org/apache/poi/xssf/usermodel/TestXSSFBugs.java
index aff4e21f97..6fe63c5e94 100644
--- a/src/ooxml/testcases/org/apache/poi/xssf/usermodel/TestXSSFBugs.java
+++ b/src/ooxml/testcases/org/apache/poi/xssf/usermodel/TestXSSFBugs.java
@@ -3450,6 +3450,60 @@ public final class TestXSSFBugs extends BaseTestBugzillaIssues {
             assertEquals(1, numMergedRegions);
             assertEquals(1, ctMergeCellCount);
             assertEquals(1, ctMergeCellListSize);
+
+        }
+    }
+
+    @Test
+    public void bug60397() throws IOException {
+        try (XSSFWorkbook wb = new XSSFWorkbook()) {
+            XSSFSheet sheet = wb.createSheet();
+
+            CellRangeAddress region = new CellRangeAddress(1, 1, 1, 2);
+            assertEquals(0, sheet.addMergedRegion(region));
+            //System.out.println(String.format("%s: index=%d", "testAddMergedRegion", index));
+
+            List<CellRangeAddress> ranges = sheet.getMergedRegions();
+            int numMergedRegions = sheet.getNumMergedRegions();
+            CTWorksheet ctSheet = sheet.getCTWorksheet();
+            CTMergeCells ctMergeCells = ctSheet.getMergeCells();
+            List<CTMergeCell> ctMergeCellList = ctMergeCells.getMergeCellList();
+            long ctMergeCellCount = ctMergeCells.getCount();
+            int ctMergeCellListSize = ctMergeCellList.size();
+
+            /*System.out.println(String.format("\ntestMergeRegions(%s)", "After adding first region"));
+            System.out.println(String.format("ranges.size=%d", ranges.size()));
+            System.out.println(String.format("numMergedRegions=%d", numMergedRegions));
+            System.out.println(String.format("ctMergeCellCount=%d", ctMergeCellCount));
+            System.out.println(String.format("ctMergeCellListSize=%d", ctMergeCellListSize)); */
+
+            assertEquals(1, ranges.size());
+            assertEquals(1, numMergedRegions);
+            assertEquals(1, ctMergeCellCount);
+            assertEquals(1, ctMergeCellListSize);
+
+            CellRangeAddress region2 = new CellRangeAddress(1, 2, 4, 6);
+            assertEquals(1, sheet.addMergedRegion(region2));
+            //System.out.println(String.format("%s: index=%d", "testAddMergedRegion", index));
+
+            ranges = sheet.getMergedRegions();
+            numMergedRegions = sheet.getNumMergedRegions();
+            ctSheet = sheet.getCTWorksheet();
+            ctMergeCells = ctSheet.getMergeCells();
+            ctMergeCellList = ctMergeCells.getMergeCellList();
+            ctMergeCellCount = ctMergeCells.getCount();
+            ctMergeCellListSize = ctMergeCellList.size();
+
+            /*System.out.println(String.format("\ntestMergeRegions(%s)", "After adding second region"));
+            System.out.println(String.format("ranges.size=%d", ranges.size()));
+            System.out.println(String.format("numMergedRegions=%d", numMergedRegions));
+            System.out.println(String.format("ctMergeCellCount=%d", ctMergeCellCount));
+            System.out.println(String.format("ctMergeCellListSize=%d", ctMergeCellListSize));*/
+
+            assertEquals(2, ranges.size());
+            assertEquals(2, numMergedRegions);
+            assertEquals(2, ctMergeCellCount);
+            assertEquals(2, ctMergeCellListSize);
         }
     }