diff --git a/src/Analyser/NodeScopeResolver.php b/src/Analyser/NodeScopeResolver.php
index 0c708a4068..b1826cffd5 100644
--- a/src/Analyser/NodeScopeResolver.php
+++ b/src/Analyser/NodeScopeResolver.php
@@ -6808,8 +6808,39 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 		}
 
 		$additionalExpressions = [];
-		$offsetValueType = $valueToWrite;
 		$lastDimKey = array_key_last($dimFetchStack);
+
+		// Compute improved intermediate types bottom-up using scope types.
+		// The top-down derivation from the root type loses constant array
+		// precision (e.g. array{-1: 0, 0: 0} becomes array<-1|0, int>).
+		// By applying the write to the scope's tracked constant array type,
+		// we preserve the constant array structure through loop generalization.
+		$improvedTypes = [];
+		$childPostWriteType = $originalValueToWrite;
+		for ($key = ($lastDimKey ?? 0) - 1; $key >= 0; $key--) {
+			$dimFetch = $dimFetchStack[$key];
+			if ($dimFetch->dim === null) {
+				break;
+			}
+
+			$nextDimFetch = $dimFetchStack[$key + 1];
+			if ($nextDimFetch->dim === null || !$scope->hasExpressionType($dimFetch)->yes()) {
+				break;
+			}
+
+			$scopeType = $scope->getType($dimFetch);
+			$childOffset = $scope->getType($nextDimFetch->dim);
+
+			if (!$scopeType->hasOffsetValueType($childOffset)->yes()) {
+				break;
+			}
+
+			$improvedType = $scopeType->setExistingOffsetValueType($childOffset, $childPostWriteType);
+			$improvedTypes[$key] = $improvedType;
+			$childPostWriteType = $improvedType;
+		}
+
+		$offsetValueType = $valueToWrite;
 		foreach ($dimFetchStack as $key => $dimFetch) {
 			if ($dimFetch->dim === null) {
 				continue;
@@ -6817,6 +6848,8 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 
 			if ($key === $lastDimKey) {
 				$offsetValueType = $originalValueToWrite;
+			} elseif (isset($improvedTypes[$key])) {
+				$offsetValueType = $improvedTypes[$key];
 			} else {
 				$offsetType = $scope->getType($dimFetch->dim);
 				$offsetValueType = $offsetValueType->getOffsetValueType($offsetType);
diff --git a/tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php b/tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php
index 73d4f028e0..a45ba6b00c 100644
--- a/tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php
+++ b/tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php
@@ -1145,4 +1145,11 @@ public function testBug11276(): void
 		$this->analyse([__DIR__ . '/data/bug-11276.php'], []);
 	}
 
+	public function testBug13669(): void
+	{
+		$this->reportPossiblyNonexistentGeneralArrayOffset = true;
+
+		$this->analyse([__DIR__ . '/data/bug-13669.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Arrays/data/bug-13669.php b/tests/PHPStan/Rules/Arrays/data/bug-13669.php
new file mode 100644
index 0000000000..a24c31b2d8
--- /dev/null
+++ b/tests/PHPStan/Rules/Arrays/data/bug-13669.php
@@ -0,0 +1,50 @@
+<?php declare(strict_types = 1);
+
+namespace Bug13669;
+
+final class Foo
+{
+	/**
+	 * @var array<int, array<MailStatus::CODE_*, int>>
+	 */
+	private array $mailCounts;
+
+	/** @var array<int, array<MailStatus::CODE_*>> */
+	private array $sources;
+
+	/** @param array<int, array<MailStatus::CODE_*>> $sources */
+	private function __construct(array $sources)
+	{
+		$this->mailCounts = [];
+		$this->sources = $sources;
+	}
+
+
+	public function countMailStates(): void
+	{
+		foreach ($this->sources as $templateId => $mails) {
+			$this->mailCounts[$templateId] = [
+				MailStatus::CODE_DELETED => 0,
+				MailStatus::CODE_NOT_ACTIVE => 0,
+				MailStatus::CODE_ACTIVE => 0,
+				MailStatus::CODE_SIMULATION => 0,
+			];
+
+			foreach ($mails as $mail) {
+				++$this->mailCounts[$templateId][$mail];
+			}
+		}
+	}
+
+}
+
+final class MailStatus
+{
+	public const CODE_DELETED = -1;
+
+	public const CODE_NOT_ACTIVE = 0;
+
+	public const CODE_SIMULATION = 1;
+
+	public const CODE_ACTIVE = 2;
+}
diff --git a/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php b/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php
index fb1b119745..3cb6904e0e 100644
--- a/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php
+++ b/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php
@@ -821,4 +821,22 @@ public function testBug10595(): void
 		$this->analyse([__DIR__ . '/data/bug-10595.php'], []);
 	}
 
+	public function testBug10349(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-10349.php'], [
+			[
+				'Binary operation "+=" between bool|float|int|string and int results in an error.',
+				17,
+			],
+			[
+				'Binary operation "+=" between bool|float|int|string and int results in an error.',
+				42,
+			],
+			[
+				'Binary operation "+=" between bool|float|int|string and int results in an error.',
+				59,
+			],
+		]);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Operators/data/bug-10349.php b/tests/PHPStan/Rules/Operators/data/bug-10349.php
new file mode 100644
index 0000000000..4ce3b96535
--- /dev/null
+++ b/tests/PHPStan/Rules/Operators/data/bug-10349.php
@@ -0,0 +1,68 @@
+<?php
+
+namespace Bug10349;
+
+class Foo
+{
+	/**
+	 * @param int $ptr
+	 * @param array<int, array<string, scalar>> $expected
+	 *
+	 * @return array<int, array<string, scalar>>
+	 */
+	private function issue_1_A($ptr, $expected)
+	{
+		foreach ($expected as $key => $param) {
+			if ($param['number-1'] !== false) {
+				$expected[$key]['number-1'] += $ptr;
+			}
+
+			if ($param['number-2'] !== false) {
+				$expected[$key]['number-2'] += $ptr;
+			}
+		}
+
+		return $expected;
+	}
+
+	/**
+	 * @param int $ptr
+	 * @param array<int, array<string, scalar>> $expected
+	 *
+	 * @return array<int, array<string, scalar>>
+	 */
+	private function issue_1_B($ptr, $expected)
+	{
+		foreach ($expected as $key => $param) {
+			if (is_int($expected[$key]['number-1'])) {
+				$expected[$key]['number-1'] += $ptr;
+			}
+
+			if ($param['number-2'] !== false) {
+				$expected[$key]['number-2'] += $ptr;
+			}
+		}
+
+		return $expected;
+	}
+
+	/**
+	 * @param int $ptr
+	 * @param array<int, array<string, scalar>> $expected
+	 *
+	 * @return array<int, array<string, scalar>>
+	 */
+	private function issue_2($ptr, $expected)
+	{
+		foreach ($expected as $key => $param) {
+			if (is_int($param['number-1'])) {
+				$expected[$key]['number-1'] += $ptr;
+			}
+			if (is_int($param['number-2'])) {
+				$expected[$key]['number-2'] += $ptr;
+			}
+		}
+
+		return $expected;
+	}
+}