diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
index 3b6047abb9..729e8726c7 100644
--- a/phpstan-baseline.neon
+++ b/phpstan-baseline.neon
@@ -838,7 +838,7 @@ parameters:
 
 		-
 			message: "#^Doing instanceof PHPStan\\\\Type\\\\Constant\\\\ConstantStringType is error\\-prone and deprecated\\. Use Type\\:\\:getConstantStrings\\(\\) instead\\.$#"
-			count: 4
+			count: 3
 			path: src/Type/Constant/ConstantArrayType.php
 
 		-
@@ -846,11 +846,6 @@ parameters:
 			count: 1
 			path: src/Type/Constant/ConstantArrayType.php
 
-		-
-			message: "#^Doing instanceof PHPStan\\\\Type\\\\StringType is error\\-prone and deprecated\\. Use Type\\:\\:isString\\(\\) instead\\.$#"
-			count: 1
-			path: src/Type/Constant/ConstantArrayType.php
-
 		-
 			message: "#^Doing instanceof PHPStan\\\\Type\\\\Constant\\\\ConstantStringType is error\\-prone and deprecated\\. Use Type\\:\\:getConstantStrings\\(\\) instead\\.$#"
 			count: 2
diff --git a/src/Type/Constant/ConstantArrayType.php b/src/Type/Constant/ConstantArrayType.php
index 5581cc9abd..822681c888 100644
--- a/src/Type/Constant/ConstantArrayType.php
+++ b/src/Type/Constant/ConstantArrayType.php
@@ -40,7 +40,6 @@
 use PHPStan\Type\IntersectionType;
 use PHPStan\Type\MixedType;
 use PHPStan\Type\NeverType;
-use PHPStan\Type\StringType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
 use PHPStan\Type\UnionType;
@@ -619,8 +618,8 @@ public function hasOffsetValueType(Type $offsetType): TrinaryLogic
 		foreach ($this->keyTypes as $i => $keyType) {
 			if (
 				$keyType instanceof ConstantIntegerType
-				&& $offsetType instanceof StringType
-				&& !$offsetType instanceof ConstantStringType
+				&& !$offsetType->isString()->no()
+				&& $offsetType->isConstantScalarValue()->no()
 			) {
 				return TrinaryLogic::createMaybe();
 			}
diff --git a/tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php b/tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php
index 613770aead..8a32d8bd92 100644
--- a/tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php
+++ b/tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php
@@ -368,4 +368,12 @@ public function testBug8084(): void
 		$this->analyse([__DIR__ . '/data/bug-8084.php'], []);
 	}
 
+	public function testBug10577(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->strictUnnecessaryNullsafePropertyFetch = true;
+
+		$this->analyse([__DIR__ . '/data/bug-10577.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Variables/data/bug-10577.php b/tests/PHPStan/Rules/Variables/data/bug-10577.php
new file mode 100644
index 0000000000..0cc67d11c8
--- /dev/null
+++ b/tests/PHPStan/Rules/Variables/data/bug-10577.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace Bug10577;
+
+class HelloWorld
+{
+	private const MAP = [
+		'10' => 'Test1',
+		'20' => 'Test2',
+	];
+
+
+	public function validate(string $value): void
+	{
+		$value = trim($value);
+
+		if ($value === '') {
+			throw new \RuntimeException();
+		}
+
+		$value = self::MAP[$value] ?? $value;
+
+		// ...
+	}
+}