diff --git a/src/PhpSpreadsheet/Calculation/Calculation.php b/src/PhpSpreadsheet/Calculation/Calculation.php
index 04b5c5e1bf..bcd993be82 100644
--- a/src/PhpSpreadsheet/Calculation/Calculation.php
+++ b/src/PhpSpreadsheet/Calculation/Calculation.php
@@ -850,16 +850,15 @@ private static function resizeMatricesExtend(array &$matrix1, array &$matrix2, i
         if (($matrix2Columns < $matrix1Columns) || ($matrix2Rows < $matrix1Rows)) {
             if ($matrix2Columns < $matrix1Columns) {
                 for ($i = 0; $i < $matrix2Rows; ++$i) {
-                    /** @var mixed[][] $matrix2 */
-                    $x = $matrix2[$i][$matrix2Columns - 1];
+                    $x = ($matrix2Columns === 1) ? $matrix2[$i][0] : null;
                     for ($j = $matrix2Columns; $j < $matrix1Columns; ++$j) {
                         $matrix2[$i][$j] = $x;
                     }
                 }
             }
             if ($matrix2Rows < $matrix1Rows) {
-                $x = $matrix2[$matrix2Rows - 1];
-                for ($i = 0; $i < $matrix1Rows; ++$i) {
+                $x = ($matrix2Rows === 1) ? $matrix2[0] : array_fill(0, $matrix2Columns, null);
+                for ($i = $matrix2Rows; $i < $matrix1Rows; ++$i) {
                     $matrix2[$i] = $x;
                 }
             }
@@ -868,16 +867,15 @@ private static function resizeMatricesExtend(array &$matrix1, array &$matrix2, i
         if (($matrix1Columns < $matrix2Columns) || ($matrix1Rows < $matrix2Rows)) {
             if ($matrix1Columns < $matrix2Columns) {
                 for ($i = 0; $i < $matrix1Rows; ++$i) {
-                    /** @var mixed[][] $matrix1 */
-                    $x = $matrix1[$i][$matrix1Columns - 1];
+                    $x = ($matrix1Columns === 1) ? $matrix1[$i][0] : null;
                     for ($j = $matrix1Columns; $j < $matrix2Columns; ++$j) {
                         $matrix1[$i][$j] = $x;
                     }
                 }
             }
             if ($matrix1Rows < $matrix2Rows) {
-                $x = $matrix1[$matrix1Rows - 1];
-                for ($i = 0; $i < $matrix2Rows; ++$i) {
+                $x = ($matrix1Rows === 1) ? $matrix1[0] : array_fill(0, $matrix1Columns, null);
+                for ($i = $matrix1Rows; $i < $matrix2Rows; ++$i) {
                     $matrix1[$i] = $x;
                 }
             }
@@ -2367,16 +2365,14 @@ private function executeNumericBinaryOperation(mixed $operand1, mixed $operand2,
 
             for ($row = 0; $row < $rows; ++$row) {
                 for ($column = 0; $column < $columns; ++$column) {
-                    /** @var mixed[][] $operand1 */
-                    if ($operand1[$row][$column] === null) {
+                    if (($operand1[$row][$column] ?? null) === null) {
                         $operand1[$row][$column] = 0;
                     } elseif (!self::isNumericOrBool($operand1[$row][$column])) {
                         $operand1[$row][$column] = self::makeError($operand1[$row][$column]);
 
                         continue;
                     }
-                    /** @var mixed[][] $operand2 */
-                    if ($operand2[$row][$column] === null) {
+                    if (($operand2[$row][$column] ?? null) === null) {
                         $operand2[$row][$column] = 0;
                     } elseif (!self::isNumericOrBool($operand2[$row][$column])) {
                         $operand1[$row][$column] = self::makeError($operand2[$row][$column]);
diff --git a/src/PhpSpreadsheet/Calculation/LookupRef/Filter.php b/src/PhpSpreadsheet/Calculation/LookupRef/Filter.php
index daedcd0b9f..1a2553beb6 100644
--- a/src/PhpSpreadsheet/Calculation/LookupRef/Filter.php
+++ b/src/PhpSpreadsheet/Calculation/LookupRef/Filter.php
@@ -45,7 +45,7 @@ private static function filterByRow(array $lookupArray, array $matchArray): arra
 
         return array_filter(
             array_values($lookupArray),
-            fn ($index): bool => (bool) $matchArray[$index],
+            fn ($index): bool => (bool) ($matchArray[$index] ?? null),
             ARRAY_FILTER_USE_KEY
         );
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Issue4451Test.php b/tests/PhpSpreadsheetTests/Calculation/Issue4451Test.php
new file mode 100644
index 0000000000..3b9107d18f
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Calculation/Issue4451Test.php
@@ -0,0 +1,128 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpOffice\PhpSpreadsheetTests\Calculation;
+
+use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PHPUnit\Framework\TestCase;
+use ReflectionMethod;
+
+class Issue4451Test extends TestCase
+{
+    public static function testReflect(): void
+    {
+        // Sample matrices to test with
+        $matrix1 = [[1], [3]];
+        $matrix2 = [[5], [8], [11]];
+
+        // Use reflection to make the protected method accessible
+        $calculation = new Calculation();
+        $reflectionMethod = new ReflectionMethod(Calculation::class, 'resizeMatricesExtend');
+        $reflectionMethod->setAccessible(true);
+
+        // Call the method using reflection
+        $reflectionMethod->invokeArgs($calculation, [&$matrix1, &$matrix2, count($matrix1), 1, count($matrix2), 1]);
+
+        self::assertSame([[1], [3], [null]], $matrix1); //* @phpstan-ignore-line
+    }
+
+    /**
+     * These 2 tests are contrived. They prove that method
+     * works as desired, but Excel will actually return
+     * a CALC error, a result I don't know how to duplicate.
+     */
+    public static function testExtendFirstColumn(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+        $sheet->setTitle('Products');
+        $calculationEngine = Calculation::getInstance($spreadsheet);
+        $calculationEngine->setInstanceArrayReturnType(
+            Calculation::RETURN_ARRAY_AS_ARRAY
+        );
+
+        $sheet->getCell('D5')->setValue(5);
+        $sheet->getCell('E5')->setValue(20);
+        $sheet->fromArray(
+            [
+                [5, 20, 'Apples'],
+                [10, 20, 'Bananas'],
+                [5, 20, 'Cherries'],
+                [5, 40, 'Grapes'],
+                [25, 50, 'Peaches'],
+                [30, 60, 'Pears'],
+                [35, 70, 'Papayas'],
+                [40, 80, 'Mangos'],
+                [null, 20, 'Unknown'],
+            ],
+            null,
+            'K1',
+            true
+        );
+        $kRows = $sheet->getHighestDataRow('K');
+        self::assertSame(8, $kRows);
+        $lRows = $sheet->getHighestDataRow('L');
+        self::assertSame(9, $lRows);
+        $mRows = $sheet->getHighestDataRow('M');
+        self::assertSame(9, $mRows);
+        $sheet->getCell('A1')
+            ->setValue(
+                "=FILTER(Products!M1:M$mRows,"
+                    . "(Products!K1:K$kRows=D5)"
+                    . "*(Products!L1:L$lRows=E5))"
+            );
+
+        $result = $sheet->getCell('A1')->getCalculatedValue();
+        self::assertSame([['Apples'], ['Cherries']], $result);
+        $spreadsheet->disconnectWorksheets();
+    }
+
+    public static function testExtendSecondColumn(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+        $sheet->setTitle('Products');
+        $calculationEngine = Calculation::getInstance($spreadsheet);
+        $calculationEngine->setInstanceArrayReturnType(
+            Calculation::RETURN_ARRAY_AS_ARRAY
+        );
+
+        $sheet->getCell('D5')->setValue(5);
+        $sheet->getCell('E5')->setValue(20);
+        $sheet->fromArray(
+            [
+                [5, 20, 'Apples'],
+                [10, 20, 'Bananas'],
+                [5, 20, 'Cherries'],
+                [5, 40, 'Grapes'],
+                [25, 50, 'Peaches'],
+                [30, 60, 'Pears'],
+                [35, 70, 'Papayas'],
+                [40, 80, 'Mangos'],
+                [null, 20, 'Unknown'],
+            ],
+            null,
+            'K1',
+            true
+        );
+        $kRows = $sheet->getHighestDataRow('K');
+        self::assertSame(8, $kRows);
+        //$lRows = $sheet->getHighestDataRow('L');
+        //self::assertSame(9, $lRows);
+        $lRows = 2;
+        $mRows = $sheet->getHighestDataRow('M');
+        self::assertSame(9, $mRows);
+        $sheet->getCell('A1')
+            ->setValue(
+                "=FILTER(Products!M1:M$mRows,"
+                    . "(Products!K1:K$kRows=D5)"
+                    . "*(Products!L1:L$lRows=E5))"
+            );
+
+        $result = $sheet->getCell('A1')->getCalculatedValue();
+        self::assertSame([['Apples']], $result);
+        $spreadsheet->disconnectWorksheets();
+    }
+}