diff --git a/src/Reflection/InitializerExprTypeResolver.php b/src/Reflection/InitializerExprTypeResolver.php
index 7332aab8f3..0b2c527049 100644
--- a/src/Reflection/InitializerExprTypeResolver.php
+++ b/src/Reflection/InitializerExprTypeResolver.php
@@ -649,27 +649,71 @@ public function getArrayType(Expr\Array_ $expr, callable $getTypeCallback): Type
 			$valueType = $getTypeCallback($arrayItem->value);
 			if ($arrayItem->unpack) {
 				$constantArrays = $valueType->getConstantArrays();
-				if (count($constantArrays) === 1) {
-					$constantArrayType = $constantArrays[0];
-
-					$hasStringKey = false;
-					if ($this->phpVersion->supportsArrayUnpackingWithStringKeys()) {
-						foreach ($constantArrayType->getKeyTypes() as $keyType) {
-							if ($keyType->isString()->yes()) {
-								$hasStringKey = true;
-								break;
+				if (count($constantArrays) > 0) {
+					$keepStringKeys = $this->phpVersion->supportsArrayUnpackingWithStringKeys();
+					$totalArrays = count($constantArrays);
+
+					// Unpacking merges string keys by name, while integer keys are always
+					// renumbered, so they're merged by their position among integer keys.
+					// A slot missing from some of the unpacked arrays becomes optional.
+					/** @var array<string, array{keyType: ConstantStringType|null, valueTypes: list<Type>, presentCount: int, anyOptional: bool}> $slots */
+					$slots = [];
+					/** @var list<string> $slotOrder */
+					$slotOrder = [];
+
+					foreach ($constantArrays as $constantArrayType) {
+						$nextIntegerSlot = 0;
+						foreach ($constantArrayType->getKeyTypes() as $i => $keyType) {
+							if ($keepStringKeys && $keyType->isString()->yes()) {
+								$slotKey = 's' . $keyType->getValue();
+								$slotKeyType = $keyType;
+							} else {
+								$slotKey = 'i' . $nextIntegerSlot;
+								$slotKeyType = null;
+								$nextIntegerSlot++;
+							}
+
+							if (!isset($slots[$slotKey])) {
+								$slots[$slotKey] = [
+									'keyType' => $slotKeyType,
+									'valueTypes' => [],
+									'presentCount' => 0,
+									'anyOptional' => false,
+								];
+								$slotOrder[] = $slotKey;
 							}
-						}
-					}
 
-					foreach ($constantArrayType->getValueTypes() as $i => $innerValueType) {
-						if ($hasStringKey) {
-							$arrayBuilder->setOffsetValueType($constantArrayType->getKeyTypes()[$i], $innerValueType, $constantArrayType->isOptionalKey($i));
+							$slots[$slotKey]['valueTypes'][] = $constantArrayType->getValueTypes()[$i];
+							$slots[$slotKey]['presentCount']++;
 							if (!$constantArrayType->isOptionalKey($i)) {
-								$hasOffsetValueTypes[$constantArrayType->getKeyTypes()[$i]->getValue()] = new HasOffsetValueType($constantArrayType->getKeyTypes()[$i], $innerValueType);
+								continue;
 							}
-						} else {
-							$arrayBuilder->setOffsetValueType(null, $innerValueType, $constantArrayType->isOptionalKey($i));
+
+							$slots[$slotKey]['anyOptional'] = true;
+						}
+					}
+
+					foreach ($slotOrder as $slotKey) {
+						$slot = $slots[$slotKey];
+						$mergedValueType = TypeCombinator::union(...$slot['valueTypes']);
+						$isOptional = $slot['anyOptional'] || $slot['presentCount'] < $totalArrays;
+						$slotKeyType = $slot['keyType'];
+						$arrayBuilder->setOffsetValueType($slotKeyType, $mergedValueType, $isOptional);
+
+						if ($slotKeyType === null) {
+							continue;
+						}
+
+						$keyValue = $slotKeyType->getValue();
+						if (isset($hasOffsetValueTypes[$keyValue])) {
+							$hasOffsetValueTypes[$keyValue] = new HasOffsetValueType(
+								$slotKeyType,
+								$isOptional
+									? TypeCombinator::union($hasOffsetValueTypes[$keyValue]->getValueType(), $mergedValueType)
+									: $mergedValueType,
+							);
+						} elseif (!$isOptional) {
+							$hasOffsetValueTypes[$keyValue] = new HasOffsetValueType($slotKeyType, $mergedValueType);
 						}
 					}
 				} else {
diff --git a/tests/PHPStan/Analyser/nsrt/array-unpacking-string-keys.php b/tests/PHPStan/Analyser/nsrt/array-unpacking-string-keys.php
index a03dbb75c9..1495bb711d 100644
--- a/tests/PHPStan/Analyser/nsrt/array-unpacking-string-keys.php
+++ b/tests/PHPStan/Analyser/nsrt/array-unpacking-string-keys.php
@@ -12,6 +12,19 @@
 
 assertType('array{0: 1, a: 1, b: 2}', $bar);
 
+// integer keys are renumbered even when the unpacked array also has string keys
+$mixed = [9, ...['a' => 1, 5], ...[6, 'b' => 2]];
+
+assertType('array{0: 9, a: 1, 1: 5, 2: 6, b: 2}', $mixed);
+
+$mixedOnlyIntegerKeys = [9, ...[5, 6]];
+
+assertType('array{9, 5, 6}', $mixedOnlyIntegerKeys);
+
+$mixedIntegerKeysOverwritten = [9, ...[3 => 'x']];
+
+assertType("array{9, 'x'}", $mixedIntegerKeysOverwritten);
+
 /**
  * @param array<string, int> $a
  * @param array<int, int> $b
diff --git a/tests/PHPStan/Analyser/nsrt/bug-14708.php b/tests/PHPStan/Analyser/nsrt/bug-14708.php
new file mode 100644
index 0000000000..d6a659fe14
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-14708.php
@@ -0,0 +1,113 @@
+<?php // lint >= 8.1
+
+declare(strict_types = 1);
+
+namespace Bug14708;
+
+use function PHPStan\Testing\assertType;
+
+/** @return array{test: bool, spread?: true} */
+function test1(bool $spread): array {
+	$result = [
+		'test' => $spread,
+		...($spread ? ['spread' => true] : []),
+	];
+	assertType('array{test: bool, spread?: true}', $result);
+	return $result;
+}
+
+/** @return array{test: bool, spread?: true} */
+function test2(bool $spread): array {
+	$return1 = ['test' => $spread];
+	$return2 = $spread ? ['spread' => true] : [];
+
+	$result = [...$return1, ...$return2];
+	assertType('array{test: bool, spread?: true}', $result);
+	return $result;
+}
+
+/** @return array{test: bool, spread?: true} */
+function test3(bool $spread): array {
+	$return = ['test' => $spread];
+	if ($spread) {
+		$return['spread'] = true;
+	}
+
+	assertType('array{test: bool, spread?: true}', $return);
+	return $return;
+}
+
+function testMultipleOptionalKeys(bool $a, bool $b): void {
+	$result = [
+		'base' => 1,
+		...($a ? ['x' => 'hello'] : []),
+		...($b ? ['y' => 42] : []),
+	];
+	assertType("array{base: 1, x?: 'hello', y?: 42}", $result);
+}
+
+function testOverlappingKeys(bool $flag): void {
+	$result = [
+		'a' => 1,
+		...($flag ? ['a' => 2, 'b' => 3] : ['b' => 4]),
+	];
+	assertType('array{a: 1|2, b: 3|4}', $result);
+}
+
+function testIntegerKeysUnion(bool $flag): void {
+	$result = [
+		'start' => 0,
+		...($flag ? [1, 2] : [3]),
+	];
+	assertType('array{start: 0, 0: 1|3, 1?: 2}', $result);
+}
+
+function testAllBranchesSameKeys(bool $flag): void {
+	$result = [
+		...($flag ? ['a' => 1, 'b' => 2] : ['a' => 3, 'b' => 4]),
+	];
+	assertType('array{a: 1|3, b: 2|4}', $result);
+}
+
+/** @param 'x'|'y'|'z' $variant */
+function testThreeBranchUnion(string $variant): void {
+	if ($variant === 'x') {
+		$extra = ['x' => 1];
+	} elseif ($variant === 'y') {
+		$extra = ['y' => 2];
+	} else {
+		$extra = [];
+	}
+	$result = ['base' => true, ...$extra];
+	assertType('array{base: true, y?: 2, x?: 1}', $result);
+}
+
+function testIntegerOnlyUnion(bool $flag): void {
+	$result = [
+		...($flag ? [1, 2, 3] : [4, 5]),
+	];
+	assertType('array{0: 1|4, 1: 2|5, 2?: 3}', $result);
+}
+
+function testEmptyVsNonEmpty(bool $flag): void {
+	$result = [
+		...($flag ? ['key' => 'value'] : []),
+	];
+	assertType("array{key?: 'value'}", $result);
+}
+
+function testStringKeyBranchAndIntegerKeyBranch(bool $flag): void {
+	// integer keys are renumbered, string keys are kept
+	$result = [
+		9,
+		...($flag ? ['a' => 1] : [5]),
+	];
+	assertType('array{0: 9, a?: 1, 1?: 5}', $result);
+}
+
+function testMixedKeysInBothBranches(bool $flag): void {
+	$result = [
+		...($flag ? ['a' => 1, 7] : [5, 'a' => 2]),
+	];
+	assertType('array{a: 1|2, 0: 5|7}', $result);
+}