diff --git a/src/Type/ArrayType.php b/src/Type/ArrayType.php
index ffd213eb93..320b22ad3b 100644
--- a/src/Type/ArrayType.php
+++ b/src/Type/ArrayType.php
@@ -268,6 +268,9 @@ public function looseCompare(Type $type, PhpVersion $phpVersion): BooleanType
 	public function hasOffsetValueType(Type $offsetType): TrinaryLogic
 	{
 		$offsetType = $offsetType->toArrayKey();
+		if ($offsetType instanceof ErrorType) {
+			return TrinaryLogic::createNo();
+		}
 
 		if ($this->getKeyType()->isSuperTypeOf($offsetType)->no()
 			&& ($offsetType->isString()->no() || !$offsetType->isConstantScalarValue()->no())
diff --git a/src/Type/Constant/ConstantArrayType.php b/src/Type/Constant/ConstantArrayType.php
index 5643e79655..bba9e8b8a6 100644
--- a/src/Type/Constant/ConstantArrayType.php
+++ b/src/Type/Constant/ConstantArrayType.php
@@ -588,6 +588,10 @@ public function hasOffsetValueType(Type $offsetType): TrinaryLogic
 
 	private function recursiveHasOffsetValueType(Type $offsetType): TrinaryLogic
 	{
+		if ($offsetType instanceof ErrorType) {
+			return TrinaryLogic::createNo();
+		}
+
 		if ($offsetType instanceof UnionType) {
 			$results = [];
 			foreach ($offsetType->getTypes() as $innerType) {
diff --git a/src/Type/ObjectType.php b/src/Type/ObjectType.php
index 78e4473410..43b277774f 100644
--- a/src/Type/ObjectType.php
+++ b/src/Type/ObjectType.php
@@ -702,7 +702,7 @@ public function toArray(): Type
 
 	public function toArrayKey(): Type
 	{
-		return $this->toString();
+		return new ErrorType();
 	}
 
 	public function toCoercedArgumentType(bool $strictTypes): Type
diff --git a/src/Type/Traits/ObjectTypeTrait.php b/src/Type/Traits/ObjectTypeTrait.php
index c600f2d74a..d8a52c200d 100644
--- a/src/Type/Traits/ObjectTypeTrait.php
+++ b/src/Type/Traits/ObjectTypeTrait.php
@@ -19,7 +19,6 @@
 use PHPStan\Type\BooleanType;
 use PHPStan\Type\ErrorType;
 use PHPStan\Type\MixedType;
-use PHPStan\Type\StringType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
 
@@ -271,7 +270,7 @@ public function toArray(): Type
 
 	public function toArrayKey(): Type
 	{
-		return new StringType();
+		return new ErrorType();
 	}
 
 	public function toCoercedArgumentType(bool $strictTypes): Type
diff --git a/tests/PHPStan/Analyser/LegacyNodeScopeResolverTest.php b/tests/PHPStan/Analyser/LegacyNodeScopeResolverTest.php
index 24ab77c1a0..4fdbfb9e8c 100644
--- a/tests/PHPStan/Analyser/LegacyNodeScopeResolverTest.php
+++ b/tests/PHPStan/Analyser/LegacyNodeScopeResolverTest.php
@@ -1801,7 +1801,7 @@ public static function dataProperties(): array
 				'$this->resource',
 			],
 			[
-				'mixed',
+				'*ERROR*',
 				'$this->yetAnotherAnotherMixedParameter',
 			],
 			[
diff --git a/tests/PHPStan/Levels/data/stringOffsetAccess-3.json b/tests/PHPStan/Levels/data/stringOffsetAccess-3.json
index be9fa763e2..f7f4afafdd 100644
--- a/tests/PHPStan/Levels/data/stringOffsetAccess-3.json
+++ b/tests/PHPStan/Levels/data/stringOffsetAccess-3.json
@@ -9,9 +9,19 @@
         "line": 16,
         "ignorable": true
     },
+    {
+        "message": "Offset int|object does not exist on array{baz: 21}|array{foo: 17, bar: 19}.",
+        "line": 55,
+        "ignorable": true
+    },
     {
         "message": "Invalid array key type stdClass.",
         "line": 59,
         "ignorable": true
+    },
+    {
+        "message": "Offset stdClass does not exist on array{baz: 21}|array{foo: 17, bar: 19}.",
+        "line": 59,
+        "ignorable": true
     }
-]
\ No newline at end of file
+]
diff --git a/tests/PHPStan/Levels/data/stringOffsetAccess-7.json b/tests/PHPStan/Levels/data/stringOffsetAccess-7.json
index 5471fbcf70..2d59876920 100644
--- a/tests/PHPStan/Levels/data/stringOffsetAccess-7.json
+++ b/tests/PHPStan/Levels/data/stringOffsetAccess-7.json
@@ -9,6 +9,11 @@
         "line": 31,
         "ignorable": true
     },
+    {
+        "message": "Offset int|object might not exist on array|string.",
+        "line": 35,
+        "ignorable": true
+    },
     {
         "message": "Possibly invalid array key type int|object.",
         "line": 35,
diff --git a/tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php b/tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php
index a481085088..1c6c21e9e9 100644
--- a/tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php
+++ b/tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php
@@ -193,6 +193,10 @@ public function testStrings(): void
 				'Offset 12.34 might not exist on array|string.',
 				28,
 			],
+			[
+				'Offset int|object might not exist on array|string.',
+				32,
+			],
 		]);
 	}
 
@@ -921,6 +925,20 @@ public function testBug12593(): void
 		$this->analyse([__DIR__ . '/data/bug-12593.php'], []);
 	}
 
+	public function testBugObject(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-object.php'], [
+			[
+				'Offset int|object does not exist on array{baz: 21}|array{foo: 17, bar: 19}.',
+				12,
+			],
+			[
+				'Offset object does not exist on array<string, int>.',
+				21,
+			],
+		]);
+	}
+
 	public function testBug3747(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-3747.php'], []);
diff --git a/tests/PHPStan/Rules/Arrays/data/bug-object.php b/tests/PHPStan/Rules/Arrays/data/bug-object.php
new file mode 100644
index 0000000000..97c64062a6
--- /dev/null
+++ b/tests/PHPStan/Rules/Arrays/data/bug-object.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace BugObject;
+
+class B {
+	/**
+	 * @param array{baz: 21}|array{foo: 17, bar: 19} $array
+	 * @param int|object $key
+	 */
+	public function foo($array, $key)
+	{
+		$array[$key];
+	}
+
+	/**
+	 * @param array<string, int> $array
+	 * @param object $key
+	 */
+	public function foo2($array, $key)
+	{
+		$array[$key];
+	}
+}