diff --git a/resources/RegexGrammar.pp b/resources/RegexGrammar.pp
index ba174feb29..3f49912a36 100644
--- a/resources/RegexGrammar.pp
+++ b/resources/RegexGrammar.pp
@@ -135,7 +135,7 @@
     alternation()
 
 alternation:
-    concatenation() ( ::alternation:: concatenation() #alternation )*
+    concatenation()? ( <alternation> concatenation()? #alternation )*
 
 concatenation:
     (   internal_options() | assertion() | quantification() | condition() )
@@ -154,8 +154,8 @@
         <index>
       | ::assertion_reference_:: alternation() #assertioncondition
     )
-    ::_capturing:: concatenation()?
-    ( ::alternation:: concatenation()? )?
+    ::_capturing::
+    alternation()
     ::_capturing::
 
 assertion:
@@ -165,7 +165,8 @@
       | ::lookbehind_::          #lookbehind
       | ::negative_lookbehind_:: #negativelookbehind
     )
-    alternation() ::_capturing::
+    alternation()
+    ::_capturing::
 
 quantification:
     ( class() | simple() ) ( quantifier() #quantification )?
@@ -208,7 +209,8 @@
       | ::atomic_group_:: #atomicgroup
       | ::capturing_::
     )
-    alternation() ::_capturing::
+    alternation()
+    ::_capturing::
 
 non_capturing_internal_options:
     <non_capturing_internal_option>
diff --git a/src/Command/IgnoredRegexValidator.php b/src/Command/IgnoredRegexValidator.php
index 613779b2e6..4340e0bd99 100644
--- a/src/Command/IgnoredRegexValidator.php
+++ b/src/Command/IgnoredRegexValidator.php
@@ -12,8 +12,6 @@
 use PHPStan\Type\ObjectType;
 use PHPStan\Type\VerbosityLevel;
 use function count;
-use function str_contains;
-use function str_starts_with;
 use function strrpos;
 use function substr;
 
@@ -34,19 +32,17 @@ public function validate(string $regex): IgnoredRegexValidatorResult
 		try {
 			/** @var TreeNode $ast */
 			$ast = $this->parser->parse($regex);
-		} catch (Exception $e) {
-			if (str_starts_with($e->getMessage(), 'Unexpected token "|" (alternation) at line 1')) {
-				return new IgnoredRegexValidatorResult([], false, true, '||', '\|\|');
-			}
-			if (
-				str_contains($regex, '()')
-				&& str_starts_with($e->getMessage(), 'Unexpected token ")" (_capturing) at line 1')
-			) {
-				return new IgnoredRegexValidatorResult([], false, true, '()', '\(\)');
-			}
+		} catch (Exception) {
 			return new IgnoredRegexValidatorResult([], false, false);
 		}
 
+		if (Strings::match($regex, '~(?<!\\\\)(?:\\\\\\\\)*\|\|~')) {
+			return new IgnoredRegexValidatorResult([], false, true, '||', '\|\|');
+		}
+		if (Strings::match($regex, '~(?<!\\\\)(?:\\\\\\\\)*\(\)~')) {
+			return new IgnoredRegexValidatorResult([], false, true, '()', '\(\)');
+		}
+
 		return new IgnoredRegexValidatorResult(
 			$this->getIgnoredTypes($ast),
 			$this->hasAnchorsInTheMiddle($ast),
diff --git a/src/Type/Regex/RegexGroupParser.php b/src/Type/Regex/RegexGroupParser.php
index a8a9755e8a..69eb455eaf 100644
--- a/src/Type/Regex/RegexGroupParser.php
+++ b/src/Type/Regex/RegexGroupParser.php
@@ -20,6 +20,7 @@
 use PHPStan\Type\StringType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
+use function array_values;
 use function count;
 use function in_array;
 use function is_int;
@@ -84,6 +85,9 @@ public function parseGroups(string $regex): ?array
 			return null;
 		}
 
+		$this->updateAlternationAstRemoveVerticalBarsAndAddEmptyToken($ast);
+		$this->updateCapturingAstAddEmptyToken($ast);
+
 		$captureOnlyNamed = false;
 		if ($this->phpVersion->supportsPregCaptureOnlyNamedGroups()) {
 			$captureOnlyNamed = str_contains($modifiers, 'n');
@@ -104,6 +108,51 @@ public function parseGroups(string $regex): ?array
 		return [$astWalkResult->getCapturingGroups(), $astWalkResult->getMarkVerbs()];
 	}
 
+	private function createEmptyTokenTreeNode(TreeNode $parentAst): TreeNode
+	{
+		return new TreeNode('token', ['token' => 'literal', 'value' => '', 'namespace' => 'default'], [], $parentAst);
+	}
+
+	private function updateAlternationAstRemoveVerticalBarsAndAddEmptyToken(TreeNode $ast): void
+	{
+		$children = $ast->getChildren();
+
+		foreach ($children as $i => $child) {
+			$this->updateAlternationAstRemoveVerticalBarsAndAddEmptyToken($child);
+
+			if ($ast->getId() !== '#alternation' || $child->getValueToken() !== 'alternation') {
+				continue;
+			}
+
+			unset($children[$i]);
+
+			if ($i !== 0
+				&& isset($children[$i + 1])
+				&& $children[$i + 1]->getValueToken() !== 'alternation') {
+				continue;
+			}
+
+			$children[$i] = $this->createEmptyTokenTreeNode($ast);
+		}
+
+		$ast->setChildren(array_values($children));
+	}
+
+	private function updateCapturingAstAddEmptyToken(TreeNode $ast): void
+	{
+		foreach ($ast->getChildren() as $child) {
+			$this->updateCapturingAstAddEmptyToken($child);
+		}
+
+		if ($ast->getId() !== '#capturing' || $ast->getChildren() !== []) {
+			return;
+		}
+
+		$emptyAlternationAst = new TreeNode('#alternation', null, [], $ast);
+		$emptyAlternationAst->setChildren([$this->createEmptyTokenTreeNode($emptyAlternationAst)]);
+		$ast->setChildren([$emptyAlternationAst]);
+	}
+
 	private function walkRegexAst(
 		TreeNode $ast,
 		?RegexAlternation $alternation,
diff --git a/tests/PHPStan/Analyser/nsrt/preg_match_shapes.php b/tests/PHPStan/Analyser/nsrt/preg_match_shapes.php
index 701dc1f049..8861e9f036 100644
--- a/tests/PHPStan/Analyser/nsrt/preg_match_shapes.php
+++ b/tests/PHPStan/Analyser/nsrt/preg_match_shapes.php
@@ -901,6 +901,48 @@ function bugUnescapedDashAfterRange (string $string): void
 	}
 }
 
+function bugEmptySubexpression (string $string): void {
+	if (preg_match('//', $string, $matches)) {
+		assertType("array{string}", $matches); // could be array{''}
+	}
+
+	if (preg_match('/()/', $string, $matches)) {
+		assertType("array{string, ''}", $matches); // could be array{'', ''}
+	}
+
+	if (preg_match('/|/', $string, $matches)) {
+		assertType("array{string}", $matches); // could be array{''}
+	}
+
+	if (preg_match('~|(a)~', $string, $matches)) {
+		assertType("array{0: string, 1?: 'a'}", $matches);
+	}
+
+	if (preg_match('~(a)|~', $string, $matches)) {
+		assertType("array{0: string, 1?: 'a'}", $matches);
+	}
+
+	if (preg_match('~(a)||(b)~', $string, $matches)) {
+		assertType("array{0: string, 1?: 'a'}|array{string, '', 'b'}", $matches);
+	}
+
+	if (preg_match('~(|(a))~', $string, $matches)) {
+		assertType("array{0: string, 1: ''|'a', 2?: 'a'}", $matches);
+	}
+
+	if (preg_match('~((a)|)~', $string, $matches)) {
+		assertType("array{0: string, 1: ''|'a', 2?: 'a'}", $matches);
+	}
+
+	if (preg_match('~((a)||(b))~', $string, $matches)) {
+		assertType("array{0: string, 1: ''|'a'|'b', 2?: ''|'a', 3?: 'b'}", $matches);
+	}
+
+	if (preg_match('~((a)|()|(b))~', $string, $matches)) {
+		assertType("array{0: string, 1: ''|'a'|'b', 2?: ''|'a', 3?: '', 4?: 'b'}", $matches);
+	}
+}
+
 function bug11744(string $string): void
 {
 	if (!preg_match('~^((/[a-z]+)?)~', $string, $matches)) {
diff --git a/tests/PHPStan/Command/IgnoredRegexValidatorTest.php b/tests/PHPStan/Command/IgnoredRegexValidatorTest.php
index 98a6dc58cb..39902aa01f 100644
--- a/tests/PHPStan/Command/IgnoredRegexValidatorTest.php
+++ b/tests/PHPStan/Command/IgnoredRegexValidatorTest.php
@@ -100,12 +100,48 @@ public function dataValidate(): array
 				false,
 				false,
 			],
+			[
+				'~(a\()~',
+				[],
+				false,
+				false,
+			],
+			[
+				'~b\\\()~',
+				[],
+				false,
+				true,
+			],
+			[
+				'~(c\\\\\()~',
+				[],
+				false,
+				false,
+			],
 			[
 				'~Result of || is always true.~',
 				[],
 				false,
 				true,
 			],
+			[
+				'~a\||~',
+				[],
+				false,
+				false,
+			],
+			[
+				'~b\\\||~',
+				[],
+				false,
+				true,
+			],
+			[
+				'~c\\\\\||~',
+				[],
+				false,
+				false,
+			],
 			[
 				'#Method PragmaRX\Notified\Data\Repositories\Notified::firstOrCreateByEvent() should return PragmaRX\Notified\Data\Models\Notified but returns Illuminate\Database\Eloquent\Model|null#',
 				[],