diff --git a/src/Analyser/NodeScopeResolver.php b/src/Analyser/NodeScopeResolver.php
index 12672c9d53..ecf824a240 100644
--- a/src/Analyser/NodeScopeResolver.php
+++ b/src/Analyser/NodeScopeResolver.php
@@ -5480,8 +5480,7 @@ private function processAssignVar(
 				}
 
 				if ($originalVar->dim instanceof Variable || $originalVar->dim instanceof Node\Scalar) {
-					$currentVarType = $scope->getType($originalVar);
-					if (!$originalValueToWrite->isSuperTypeOf($currentVarType)->yes()) {
+					if (!$scope->hasExpressionType($originalVar)->yes()) {
 						$scope = $scope->assignExpression(
 							$originalVar,
 							$originalValueToWrite,
diff --git a/tests/PHPStan/Analyser/NodeScopeResolverTest.php b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
index 7f3d9638b2..9dd8161487 100644
--- a/tests/PHPStan/Analyser/NodeScopeResolverTest.php
+++ b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
@@ -208,6 +208,7 @@ private static function findTestFiles(): iterable
 		yield __DIR__ . '/../Rules/Classes/data/bug-11591-property-tag.php';
 		yield __DIR__ . '/../Rules/Classes/data/mixin-trait-use.php';
 
+		yield __DIR__ . '/../Rules/Arrays/data/bug-11679.php';
 		yield __DIR__ . '/../Rules/Methods/data/bug-4801.php';
 	}
 
diff --git a/tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php b/tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php
index 78e8d86ccf..6557f97ed3 100644
--- a/tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php
+++ b/tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php
@@ -849,6 +849,20 @@ public function testArrayDimFetchOnArrayKeyFirsOrLastOrCount(): void
 		]);
 	}
 
+	public function testBug12406(): void
+	{
+		$this->reportPossiblyNonexistentGeneralArrayOffset = true;
+
+		$this->analyse([__DIR__ . '/data/bug-12406.php'], []);
+	}
+
+	public function testBug11679(): void
+	{
+		$this->reportPossiblyNonexistentGeneralArrayOffset = true;
+
+		$this->analyse([__DIR__ . '/data/bug-11679.php'], []);
+	}
+
 	public function testBug8649(): void
 	{
 		$this->reportPossiblyNonexistentGeneralArrayOffset = true;
diff --git a/tests/PHPStan/Rules/Arrays/data/bug-11679.php b/tests/PHPStan/Rules/Arrays/data/bug-11679.php
new file mode 100644
index 0000000000..463362516a
--- /dev/null
+++ b/tests/PHPStan/Rules/Arrays/data/bug-11679.php
@@ -0,0 +1,39 @@
+<?php
+
+namespace Bug11679;
+
+use function PHPStan\Testing\assertType;
+
+class WorkingExample
+{
+	/** @var array{foo?: bool} */
+	private array $arr = [];
+
+	public function sayHello(): bool
+	{
+		assertType('array{foo?: bool}', $this->arr);
+		if (!isset($this->arr['foo'])) {
+			$this->arr['foo'] = true;
+			assertType('array{foo: true}', $this->arr);
+		}
+		assertType('array{foo: bool}', $this->arr);
+		return $this->arr['foo']; // PHPStan realizes optional 'foo' is set
+	}
+}
+
+class NonworkingExample
+{
+	/** @var array<int, array{foo?: bool}> */
+	private array $arr = [];
+
+	public function sayHello(int $index): bool
+	{
+		assertType('array<int, array{foo?: bool}>', $this->arr);
+		if (!isset($this->arr[$index]['foo'])) {
+			$this->arr[$index]['foo'] = true;
+			assertType('non-empty-array<int, array{foo: true}>', $this->arr);
+		}
+		assertType('array<int, array{foo?: bool}>', $this->arr);
+		return $this->arr[$index]['foo']; // PHPStan does not realize 'foo' is set
+	}
+}
diff --git a/tests/PHPStan/Rules/Arrays/data/bug-12406.php b/tests/PHPStan/Rules/Arrays/data/bug-12406.php
new file mode 100644
index 0000000000..5d967399c1
--- /dev/null
+++ b/tests/PHPStan/Rules/Arrays/data/bug-12406.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace Bug12406;
+
+final class HelloWorld
+{
+	/** @var array<string, int> */
+	protected array $words = [];
+
+	public function sayHello(string $word, int $count): void
+	{
+		$this->words[$word] ??= 0;
+		$this->words[$word] += $count;
+	}
+}