diff --git a/src/PhpSpreadsheet/Worksheet/Worksheet.php b/src/PhpSpreadsheet/Worksheet/Worksheet.php
index 896b4e9c..51cf3c52 100644
--- a/src/PhpSpreadsheet/Worksheet/Worksheet.php
+++ b/src/PhpSpreadsheet/Worksheet/Worksheet.php
@@ -1698,27 +1698,33 @@ class Worksheet implements IComparable
     {
         // Uppercase coordinate
         $range = strtoupper($range);
+        // Convert 'A:C' to 'A1:C1048576'
+        $range = self::pregReplace('/^([A-Z]+):([A-Z]+)$/', '${1}1:${2}1048576', $range);
+        // Convert '1:3' to 'A1:XFD3'
+        $range = self::pregReplace('/^(\\d+):(\\d+)$/', 'A${1}:XFD${2}', $range);
 
-        if (strpos($range, ':') !== false) {
+        if (preg_match('/^([A-Z]+)(\\d+):([A-Z]+)(\\d+)$/', $range, $matches) === 1) {
             $this->mergeCells[$range] = $range;
-
-            // make sure cells are created
-
-            // get the cells in the range
-            $aReferences = Coordinate::extractAllCellReferencesInRange($range);
+            $firstRow = (int) $matches[2];
+            $lastRow = (int) $matches[4];
+            $firstColumn = $matches[1];
+            $lastColumn = $matches[3];
+            $firstColumnIndex = Coordinate::columnIndexFromString($firstColumn);
+            $lastColumnIndex = Coordinate::columnIndexFromString($lastColumn);
+            $numberRows = $lastRow - $firstRow;
+            $numberColumns = $lastColumnIndex - $firstColumnIndex;
 
             // create upper left cell if it does not already exist
-            $upperLeft = $aReferences[0];
+            $upperLeft = "$firstColumn$firstRow";
             if (!$this->cellExists($upperLeft)) {
                 $this->getCell($upperLeft)->setValueExplicit(null, DataType::TYPE_NULL);
             }
 
             // Blank out the rest of the cells in the range (if they exist)
-            $count = count($aReferences);
-            for ($i = 1; $i < $count; ++$i) {
-                if ($this->cellExists($aReferences[$i])) {
-                    $this->getCell($aReferences[$i])->setValueExplicit(null, DataType::TYPE_NULL);
-                }
+            if ($numberRows > $numberColumns) {
+                $this->clearMergeCellsByColumn($firstColumn, $lastColumn, $firstRow, $lastRow, $upperLeft);
+            } else {
+                $this->clearMergeCellsByRow($firstColumn, $lastColumnIndex, $firstRow, $lastRow, $upperLeft);
             }
         } else {
             throw new Exception('Merge must be set on a range of cells.');
@@ -1727,6 +1733,47 @@ class Worksheet implements IComparable
         return $this;
     }
 
+    private function clearMergeCellsByColumn(string $firstColumn, string $lastColumn, int $firstRow, int $lastRow, string $upperLeft): void
+    {
+        foreach ($this->getColumnIterator($firstColumn, $lastColumn) as $column) {
+            $iterator = $column->getCellIterator($firstRow);
+            $iterator->setIterateOnlyExistingCells(true);
+            foreach ($iterator as $cell) {
+                if ($cell !== null) {
+                    $row = $cell->getRow();
+                    if ($row > $lastRow) {
+                        break;
+                    }
+                    $thisCell = $cell->getColumn() . $row;
+                    if ($upperLeft !== $thisCell) {
+                        $cell->setValueExplicit(null, DataType::TYPE_NULL);
+                    }
+                }
+            }
+        }
+    }
+
+    private function clearMergeCellsByRow(string $firstColumn, int $lastColumnIndex, int $firstRow, int $lastRow, string $upperLeft): void
+    {
+        foreach ($this->getRowIterator($firstRow, $lastRow) as $row) {
+            $iterator = $row->getCellIterator($firstColumn);
+            $iterator->setIterateOnlyExistingCells(true);
+            foreach ($iterator as $cell) {
+                if ($cell !== null) {
+                    $column = $cell->getColumn();
+                    $columnIndex = Coordinate::columnIndexFromString($column);
+                    if ($columnIndex > $lastColumnIndex) {
+                        break;
+                    }
+                    $thisCell = $column . $cell->getRow();
+                    if ($upperLeft !== $thisCell) {
+                        $cell->setValueExplicit(null, DataType::TYPE_NULL);
+                    }
+                }
+            }
+        }
+    }
+
     /**
      * Set merge on a cell range by using numeric cell coordinates.
      *
diff --git a/tests/PhpSpreadsheetTests/Calculation/MergedCellTest.php b/tests/PhpSpreadsheetTests/Calculation/MergedCellTest.php
index 6a710436..f6e98474 100644
--- a/tests/PhpSpreadsheetTests/Calculation/MergedCellTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/MergedCellTest.php
@@ -3,43 +3,43 @@
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
+use PhpOffice\PhpSpreadsheet\Exception as SpreadException;
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PhpOffice\PhpSpreadsheet\Worksheet\Worksheet;
 use PHPUnit\Framework\TestCase;
 
 class MergedCellTest extends TestCase
 {
-    /**
-     * @var Spreadsheet
-     */
-    protected $spreadSheet;
-
-    protected function setUp(): void
-    {
-        $this->spreadSheet = new Spreadsheet();
-
-        $dataSheet = $this->spreadSheet->getActiveSheet();
-        $dataSheet->setCellValue('A1', 1.1);
-        $dataSheet->setCellValue('A2', 2.2);
-        $dataSheet->mergeCells('A2:A4');
-        $dataSheet->setCellValue('A5', 3.3);
-    }
-
     /**
      * @param mixed $expectedResult
      *
-     * @dataProvider providerWorksheetFormulae
+     * @dataProvider providerWorksheetFormulaeColumns
      */
-    public function testMergedCellBehaviour(string $formula, $expectedResult): void
+    public function testMergedCellColumns(string $formula, $expectedResult): void
     {
-        $worksheet = $this->spreadSheet->getActiveSheet();
+        $spreadSheet = new Spreadsheet();
+
+        $dataSheet = $spreadSheet->getActiveSheet();
+        $dataSheet->setCellValue('A5', 3.3);
+        $dataSheet->setCellValue('A3', 3.3);
+        $dataSheet->setCellValue('A2', 2.2);
+        $dataSheet->setCellValue('A1', 1.1);
+        $dataSheet->setCellValue('B2', 2.2);
+        $dataSheet->setCellValue('B1', 1.1);
+        $dataSheet->setCellValue('C2', 4.4);
+        $dataSheet->setCellValue('C1', 3.3);
+        $dataSheet->mergeCells('A2:A4');
+        $dataSheet->mergeCells('B:B');
+        $worksheet = $spreadSheet->getActiveSheet();
 
         $worksheet->setCellValue('A7', $formula);
 
         $result = $worksheet->getCell('A7')->getCalculatedValue();
         self::assertSame($expectedResult, $result);
+        $spreadSheet->disconnectWorksheets();
     }
 
-    public function providerWorksheetFormulae(): array
+    public function providerWorksheetFormulaeColumns(): array
     {
         return [
             ['=SUM(A1:A5)', 6.6],
@@ -48,6 +48,74 @@ class MergedCellTest extends TestCase
             ['=SUM(A3:A4)', 0],
             ['=A2+A3+A4', 2.2],
             ['=A2/A3', Functions::DIV0()],
+            ['=SUM(B1:C2)', 8.8],
         ];
     }
+
+    /**
+     * @param mixed $expectedResult
+     *
+     * @dataProvider providerWorksheetFormulaeRows
+     */
+    public function testMergedCellRows(string $formula, $expectedResult): void
+    {
+        $spreadSheet = new Spreadsheet();
+
+        $dataSheet = $spreadSheet->getActiveSheet();
+        $dataSheet->setCellValue('A1', 1.1);
+        $dataSheet->setCellValue('B1', 2.2);
+        $dataSheet->setCellValue('C1', 3.3);
+        $dataSheet->setCellValue('E1', 3.3);
+        $dataSheet->setCellValue('A2', 1.1);
+        $dataSheet->setCellValue('B2', 2.2);
+        $dataSheet->setCellValue('A3', 3.3);
+        $dataSheet->setCellValue('B3', 4.4);
+        $dataSheet->mergeCells('B1:D1');
+        $dataSheet->mergeCells('A2:B2');
+        $worksheet = $spreadSheet->getActiveSheet();
+
+        $worksheet->setCellValue('A7', $formula);
+
+        $result = $worksheet->getCell('A7')->getCalculatedValue();
+        self::assertSame($expectedResult, $result);
+        $spreadSheet->disconnectWorksheets();
+    }
+
+    public function providerWorksheetFormulaeRows(): array
+    {
+        return [
+            ['=SUM(A1:E1)', 6.6],
+            ['=COUNT(A1:E1)', 3],
+            ['=COUNTA(A1:E1)', 3],
+            ['=SUM(C1:D1)', 0],
+            ['=B1+C1+D1', 2.2],
+            ['=B1/C1', Functions::DIV0()],
+            ['=SUM(A2:B3)', 8.8],
+        ];
+    }
+
+    private function setBadRange(Worksheet $sheet, string $range): void
+    {
+        try {
+            $sheet->mergeCells($range);
+            self::fail("Expected invalid merge range $range");
+        } catch (SpreadException $e) {
+            self::assertSame('Merge must be set on a range of cells.', $e->getMessage());
+        }
+    }
+
+    public function testMergedBadRange(): void
+    {
+        $spreadSheet = new Spreadsheet();
+
+        $dataSheet = $spreadSheet->getActiveSheet();
+        $this->setBadRange($dataSheet, 'B1');
+        $this->setBadRange($dataSheet, 'Invalid');
+        $this->setBadRange($dataSheet, '1');
+        $this->setBadRange($dataSheet, 'C');
+        $this->setBadRange($dataSheet, 'B1:C');
+        $this->setBadRange($dataSheet, 'B:C2');
+
+        $spreadSheet->disconnectWorksheets();
+    }
 }
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2501Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2501Test.php
new file mode 100644
index 00000000..6b090fe8
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2501Test.php
@@ -0,0 +1,70 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
+
+use PhpOffice\PhpSpreadsheet\IOFactory;
+use PHPUnit\Framework\TestCase;
+
+class Issue2501Test extends TestCase
+{
+    /**
+     * @var string
+     */
+    private static $testbook = 'tests/data/Reader/XLSX/issue.2501.b.xlsx';
+
+    public function testPreliminaries(): void
+    {
+        $file = 'zip://';
+        $file .= self::$testbook;
+        $file .= '#xl/worksheets/sheet1.xml';
+        $data = file_get_contents($file);
+        // confirm that file contains expected merge ranges
+        if ($data === false) {
+            self::fail('Unable to read file');
+        } else {
+            self::assertStringContainsString('<mergeCells count="3"><mergeCell ref="A:A"/><mergeCell ref="B:D"/><mergeCell ref="E2:E4"/></mergeCells>', $data);
+        }
+        $file = 'zip://';
+        $file .= self::$testbook;
+        $file .= '#xl/worksheets/sheet2.xml';
+        $data = file_get_contents($file);
+        // confirm that file contains expected merged ranges
+        if ($data === false) {
+            self::fail('Unable to read file');
+        } else {
+            self::assertStringContainsString('<mergeCells count="3"><mergeCell ref="1:1"/><mergeCell ref="2:4"/><mergeCell ref="B5:D5"/></mergeCells>', $data);
+        }
+    }
+
+    public function testIssue2501(): void
+    {
+        // Merged cell range specified as 1:1"
+        $filename = self::$testbook;
+        $reader = IOFactory::createReader('Xlsx');
+        $spreadsheet = $reader->load($filename);
+        $sheet = $spreadsheet->getSheetByName('Columns');
+        $expected = [
+            'A1:A1048576',
+            'B1:D1048576',
+            'E2:E4',
+        ];
+        if ($sheet === null) {
+            self::fail('Unable to find sheet Columns');
+        } else {
+            self::assertSame($expected, array_values($sheet->getMergeCells()));
+        }
+        $sheet = $spreadsheet->getSheetByName('Rows');
+        $expected = [
+            'A1:XFD1',
+            'A2:XFD4',
+            'B5:D5',
+        ];
+        if ($sheet === null) {
+            self::fail('Unable to find sheet Rows');
+        } else {
+            self::assertSame($expected, array_values($sheet->getMergeCells()));
+        }
+
+        $spreadsheet->disconnectWorksheets();
+    }
+}
diff --git a/tests/data/Reader/XLSX/issue.2501.b.xlsx b/tests/data/Reader/XLSX/issue.2501.b.xlsx
new file mode 100644
index 00000000..fddf197b
Binary files /dev/null and b/tests/data/Reader/XLSX/issue.2501.b.xlsx differ