diff --git a/src/Type/Constant/ConstantArrayType.php b/src/Type/Constant/ConstantArrayType.php
index 3853794348..3422c8ce0b 100644
--- a/src/Type/Constant/ConstantArrayType.php
+++ b/src/Type/Constant/ConstantArrayType.php
@@ -387,6 +387,25 @@ public function isSuperTypeOf(Type $type): TrinaryLogic
 				$results[] = $isValueSuperType;
 			}
 
+			if (
+				$this->isList->yes()
+				&& $type->isList->yes()
+				&& count($this->keyTypes) !== count($type->keyTypes)
+				&& count($type->optionalKeys) === 0
+			) {
+				$keepSeparate = true;
+				foreach ($this->valueTypes as $valueType) {
+					if ($valueType->isConstantValue()->yes()) {
+						$keepSeparate = false;
+						break;
+					}
+				}
+
+				if ($keepSeparate) {
+					return TrinaryLogic::createNo();
+				}
+			}
+
 			return TrinaryLogic::createYes()->and(...$results);
 		}
 
diff --git a/tests/PHPStan/Analyser/nsrt/bug11488.php b/tests/PHPStan/Analyser/nsrt/bug11488.php
new file mode 100644
index 0000000000..b6acdaa452
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug11488.php
@@ -0,0 +1,64 @@
+<?php
+
+namespace Bug11488;
+
+use function PHPStan\Testing\assertType;
+
+class Foo
+{
+	/**
+	 * @param array{mixed}|array{0: mixed, 1?: string|null} $row
+	 */
+	protected function testOptionalKeys(array $row): void
+	{
+		if (count($row) === 1) {
+			assertType('array{0: mixed, 1?: string|null}', $row);
+		} else {
+			assertType('array{0: mixed, 1?: string|null}', $row);
+		}
+
+		if (count($row) !== 1) {
+			assertType('array{0: mixed, 1?: string|null}', $row);
+		} else {
+			assertType('array{0: mixed, 1?: string|null}', $row);
+		}
+
+		if (count($row) !== 2) {
+			assertType('array{0: mixed, 1?: string|null}', $row);
+		} else {
+			// should be array{0: mixed, 1: string|null}
+			assertType('array{mixed, mixed}', $row);
+		}
+
+		if (count($row) !== 3) {
+			// should be array{0: mixed, 1?: string|null}
+			assertType('array{0: mixed, 1?: mixed}', $row);
+		} else {
+			assertType('*NEVER*', $row);
+		}
+	}
+
+	/**
+	 * @param array{mixed}|array{mixed, string|null, mixed} $row
+	 */
+	protected function test(array $row): void
+	{
+		if (count($row) !== 1) {
+			assertType('array{mixed, string|null, mixed}', $row);
+		} else {
+			assertType('array{mixed}', $row);
+		}
+
+		if (count($row) !== 2) {
+			assertType('array{mixed, string|null, mixed}|array{mixed}', $row);
+		} else {
+			assertType('*NEVER*', $row);
+		}
+
+		if (count($row) !== 3) {
+			assertType('array{mixed}', $row);
+		} else {
+			assertType('array{mixed, string|null, mixed}', $row);
+		}
+	}
+}
diff --git a/tests/PHPStan/Type/TypeCombinatorTest.php b/tests/PHPStan/Type/TypeCombinatorTest.php
index e521c3edba..a08e10e7c9 100644
--- a/tests/PHPStan/Type/TypeCombinatorTest.php
+++ b/tests/PHPStan/Type/TypeCombinatorTest.php
@@ -4876,6 +4876,49 @@ public function dataRemove(): array
 				ObjectShapeType::class,
 				'object{foo?: int}',
 			],
+			[
+				new UnionType([
+					new ConstantArrayType(
+						[
+							new ConstantIntegerType(0),
+						],
+						[
+							new MixedType(true),
+						],
+						[0],
+						[],
+						true,
+					),
+					new ConstantArrayType(
+						[
+							new ConstantIntegerType(0),
+							new ConstantIntegerType(1),
+							new ConstantIntegerType(2),
+						],
+						[
+							new MixedType(true),
+							new UnionType([new StringType(), new NullType()]),
+							new MixedType(true),
+						],
+						[0],
+						[],
+						true,
+					),
+				]),
+				new ConstantArrayType(
+					[
+						new ConstantIntegerType(0),
+					],
+					[
+						new MixedType(true),
+					],
+					[0],
+					[],
+					true,
+				),
+				ConstantArrayType::class,
+				'array{mixed, string|null, mixed}',
+			],
 		];
 	}