diff --git a/src/Analyser/TypeSpecifier.php b/src/Analyser/TypeSpecifier.php
index 08e0c65f0c..1c1732089d 100644
--- a/src/Analyser/TypeSpecifier.php
+++ b/src/Analyser/TypeSpecifier.php
@@ -970,6 +970,11 @@ private function narrowUnionByArraySize(FuncCall $countFuncCall, UnionType $argT
 					if ($isSize->no()) {
 						continue;
 					}
+
+					$constArray = $this->turnListIntoConstantArray($countFuncCall, $innerType, $sizeType, $scope);
+					if ($constArray !== null) {
+						$innerType = $constArray;
+					}
 				}
 				if ($context->falsey()) {
 					if (!$isSize->yes()) {
@@ -986,6 +991,35 @@ private function narrowUnionByArraySize(FuncCall $countFuncCall, UnionType $argT
 		return null;
 	}
 
+	private function turnListIntoConstantArray(FuncCall $countFuncCall, Type $type, Type $sizeType, Scope $scope): ?Type
+	{
+		$argType = $scope->getType($countFuncCall->getArgs()[0]->value);
+
+		if (count($countFuncCall->getArgs()) === 1) {
+			$isNormalCount = TrinaryLogic::createYes();
+		} else {
+			$mode = $scope->getType($countFuncCall->getArgs()[1]->value);
+			$isNormalCount = (new ConstantIntegerType(COUNT_NORMAL))->isSuperTypeOf($mode)->or($argType->getIterableValueType()->isArray()->negate());
+		}
+
+		if (
+			$isNormalCount->yes()
+			&& $type->isList()->yes()
+			&& $sizeType instanceof ConstantIntegerType
+			&& $sizeType->getValue() < ConstantArrayTypeBuilder::ARRAY_COUNT_LIMIT
+		) {
+			// turn optional offsets non-optional
+			$valueTypesBuilder = ConstantArrayTypeBuilder::createEmpty();
+			for ($i = 0; $i < $sizeType->getValue(); $i++) {
+				$offsetType = new ConstantIntegerType($i);
+				$valueTypesBuilder->setOffsetValueType($offsetType, $type->getOffsetValueType($offsetType));
+			}
+			return $valueTypesBuilder->getArray();
+		}
+
+		return null;
+	}
+
 	private function specifyTypesForConstantBinaryExpression(
 		Expr $exprNode,
 		ConstantScalarType $constantType,
@@ -1050,21 +1084,18 @@ private function specifyTypesForConstantBinaryExpression(
 				}
 
 				if ($argType->isArray()->yes()) {
-					if (count($exprNode->getArgs()) === 1) {
-						$isNormalCount = TrinaryLogic::createYes();
-					} else {
-						$mode = $scope->getType($exprNode->getArgs()[1]->value);
-						$isNormalCount = (new ConstantIntegerType(COUNT_NORMAL))->isSuperTypeOf($mode)->or($argType->getIterableValueType()->isArray()->negate());
+					if (
+						$context->truthy()
+						&& $argType->isConstantArray()->yes()
+						&& $constantType->isSuperTypeOf($argType->getArraySize())->no()
+					) {
+						return $this->create($exprNode->getArgs()[0]->value, new NeverType(), $context, false, $scope, $rootExpr);
 					}
 
 					$funcTypes = $this->create($exprNode, $constantType, $context, false, $scope, $rootExpr);
-					if ($isNormalCount->yes() && $argType->isList()->yes() && $context->truthy() && $constantType->getValue() < ConstantArrayTypeBuilder::ARRAY_COUNT_LIMIT) {
-						$valueTypesBuilder = ConstantArrayTypeBuilder::createEmpty();
-						$itemType = $argType->getIterableValueType();
-						for ($i = 0; $i < $constantType->getValue(); $i++) {
-							$valueTypesBuilder->setOffsetValueType(new ConstantIntegerType($i), $itemType);
-						}
-						$valueTypes = $this->create($exprNode->getArgs()[0]->value, $valueTypesBuilder->getArray(), $context, false, $scope, $rootExpr);
+					$constArray = $this->turnListIntoConstantArray($exprNode, $argType, $constantType, $scope);
+					if ($context->truthy() && $constArray !== null) {
+						$valueTypes = $this->create($exprNode->getArgs()[0]->value, $constArray, $context, false, $scope, $rootExpr);
 					} else {
 						$valueTypes = $this->create($exprNode->getArgs()[0]->value, new NonEmptyArrayType(), $newContext, false, $scope, $rootExpr);
 					}
diff --git a/tests/PHPStan/Analyser/nsrt/list-count.php b/tests/PHPStan/Analyser/nsrt/list-count.php
index d3848ae1db..006bf149d8 100644
--- a/tests/PHPStan/Analyser/nsrt/list-count.php
+++ b/tests/PHPStan/Analyser/nsrt/list-count.php
@@ -216,3 +216,127 @@ function countCountable(CountableFoo $x, int $mode)
 	}
 	assertType('ListCount\CountableFoo', $x);
 }
+
+class CountWithOptionalKeys
+{
+	/**
+	 * @param array{0: mixed, 1?: string|null} $row
+	 */
+	protected function testOptionalKeys($row): void
+	{
+		if (count($row) === 0) {
+			assertType('*NEVER*', $row);
+		} else {
+			assertType('array{0: mixed, 1?: string|null}', $row);
+		}
+
+		if (count($row) === 1) {
+			assertType('array{mixed}', $row);
+		} else {
+			assertType('array{0: mixed, 1?: string|null}', $row);
+		}
+
+		if (count($row) === 2) {
+			assertType('array{mixed, string|null}', $row);
+		} else {
+			assertType('array{0: mixed, 1?: string|null}', $row);
+		}
+
+		if (count($row) === 3) {
+			assertType('*NEVER*', $row);
+		} else {
+			assertType('array{0: mixed, 1?: string|null}', $row);
+		}
+	}
+
+	/**
+	 * @param array{mixed}|array{0: mixed, 1?: string|null} $row
+	 */
+	protected function testOptionalKeysInUnion($row): void
+	{
+		if (count($row) === 0) {
+			assertType('*NEVER*', $row);
+		} else {
+			assertType('array{0: mixed, 1?: string|null}', $row);
+		}
+
+		if (count($row) === 1) {
+			assertType('array{mixed}', $row);
+		} else {
+			assertType('array{0: mixed, 1?: string|null}', $row);
+		}
+
+		if (count($row) === 2) {
+			assertType('array{mixed, string|null}', $row);
+		} else {
+			assertType('array{0: mixed, 1?: string|null}', $row);
+		}
+
+		if (count($row) === 3) {
+			assertType('*NEVER*', $row);
+		} else {
+			assertType('array{0: mixed, 1?: string|null}', $row);
+		}
+	}
+
+	/**
+	 * @param array{string}|array{0: int, 1?: string|null} $row
+	 */
+	protected function testOptionalKeysInListsOfTaggedUnion($row): void
+	{
+		if (count($row) === 0) {
+			assertType('*NEVER*', $row);
+		} else {
+			assertType('array{0: int, 1?: string|null}|array{string}', $row);
+		}
+
+		if (count($row) === 1) {
+			assertType('array{0: int, 1?: string|null}|array{string}', $row);
+		} else {
+			assertType('array{0: int, 1?: string|null}', $row);
+		}
+
+		if (count($row) === 2) {
+			assertType('array{int, string|null}', $row);
+		} else {
+			assertType('array{0: int, 1?: string|null}|array{string}', $row);
+		}
+
+		if (count($row) === 3) {
+			assertType('*NEVER*', $row);
+		} else {
+			assertType('array{0: int, 1?: string|null}|array{string}', $row);
+		}
+	}
+
+	/**
+	 * @param array{string}|array{0: int, 3?: string|null} $row
+	 */
+	protected function testOptionalKeysInUnionArray($row): void
+	{
+		if (count($row) === 0) {
+			assertType('*NEVER*', $row);
+		} else {
+			assertType('array{0: int, 3?: string|null}|array{string}', $row);
+		}
+
+		if (count($row) === 1) {
+			assertType('array{0: int, 3?: string|null}|array{string}', $row);
+		} else {
+			assertType('array{0: int, 3?: string|null}', $row);
+		}
+
+		if (count($row) === 2) {
+			assertType('array{0: int, 3?: string|null}', $row);
+		} else {
+			assertType('array{0: int, 3?: string|null}|array{string}', $row);
+		}
+
+		if (count($row) === 3) {
+			assertType('*NEVER*', $row);
+		} else {
+			assertType('array{0: int, 3?: string|null}|array{string}', $row);
+		}
+	}
+
+}
diff --git a/tests/PHPStan/Analyser/nsrt/preg_match_shapes.php b/tests/PHPStan/Analyser/nsrt/preg_match_shapes.php
index be26adf8b8..001ec26d21 100644
--- a/tests/PHPStan/Analyser/nsrt/preg_match_shapes.php
+++ b/tests/PHPStan/Analyser/nsrt/preg_match_shapes.php
@@ -330,7 +330,7 @@ function bug11277a(string $value): void
 	if (preg_match('/^\[(.+,?)*\]$/', $value, $matches)) {
 		assertType('array{0: string, 1?: non-empty-string}', $matches);
 		if (count($matches) === 2) {
-			assertType('array{string, string}', $matches); // could be array{string, non-empty-string}
+			assertType('array{string, non-empty-string}', $matches);
 		}
 	}
 }