diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index a43ba35dda..cf9eb75808 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -3539,6 +3539,9 @@ private function createConditionalExpressions(
 		array $mergedExpressionTypes,
 	): array
 	{
+		$globalVariableCallback = fn (Node $node) => $node instanceof Variable && is_string($node->name) && $this->isGlobalVariable($node->name);
+		$nodeFinder = new NodeFinder();
+
 		$newVariableTypes = $ourExpressionTypes;
 		foreach ($theirExpressionTypes as $exprString => $holder) {
 			if (!array_key_exists($exprString, $mergedExpressionTypes)) {
@@ -3595,6 +3598,16 @@ private function createConditionalExpressions(
 				continue;
 			}
 
+			$expr = $holder->getExpr();
+			$containsSuperGlobal = $expr->getAttribute(self::CONTAINS_SUPER_GLOBAL_ATTRIBUTE_NAME);
+			if ($containsSuperGlobal === null) {
+				$containsSuperGlobal = $nodeFinder->findFirst($expr, $globalVariableCallback) !== null;
+				$expr->setAttribute(self::CONTAINS_SUPER_GLOBAL_ATTRIBUTE_NAME, $containsSuperGlobal);
+			}
+			if ($containsSuperGlobal === true) {
+				continue;
+			}
+
 			$variableTypeGuards = $typeGuards;
 			unset($variableTypeGuards[$exprString]);
 
@@ -3622,6 +3635,16 @@ private function createConditionalExpressions(
 				continue;
 			}
 
+			$expr = $mergedExprTypeHolder->getExpr();
+			$containsSuperGlobal = $expr->getAttribute(self::CONTAINS_SUPER_GLOBAL_ATTRIBUTE_NAME);
+			if ($containsSuperGlobal === null) {
+				$containsSuperGlobal = $nodeFinder->findFirst($expr, $globalVariableCallback) !== null;
+				$expr->setAttribute(self::CONTAINS_SUPER_GLOBAL_ATTRIBUTE_NAME, $containsSuperGlobal);
+			}
+			if ($containsSuperGlobal === true) {
+				continue;
+			}
+
 			foreach ($typeGuards as $guardExprString => $guardHolder) {
 				$conditionalExpression = new ConditionalExpressionHolder([$guardExprString => $guardHolder], new ExpressionTypeHolder($mergedExprTypeHolder->getExpr(), new ErrorType(), TrinaryLogic::createNo()));
 				$conditionalExpressions[$exprString][$conditionalExpression->getKey()] = $conditionalExpression;
diff --git a/tests/PHPStan/Rules/Variables/IssetRuleTest.php b/tests/PHPStan/Rules/Variables/IssetRuleTest.php
index fd841e49b1..aef9f80458 100644
--- a/tests/PHPStan/Rules/Variables/IssetRuleTest.php
+++ b/tests/PHPStan/Rules/Variables/IssetRuleTest.php
@@ -526,6 +526,13 @@ public function testBug9503(): void
 		$this->analyse([__DIR__ . '/data/bug-9503.php'], []);
 	}
 
+	public function testBug14421(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+
+		$this->analyse([__DIR__ . '/data/bug-14421.php'], []);
+	}
+
 	public function testBug14393(): void
 	{
 		$this->treatPhpDocTypesAsCertain = true;
diff --git a/tests/PHPStan/Rules/Variables/data/bug-14421.php b/tests/PHPStan/Rules/Variables/data/bug-14421.php
new file mode 100644
index 0000000000..eafdc7068a
--- /dev/null
+++ b/tests/PHPStan/Rules/Variables/data/bug-14421.php
@@ -0,0 +1,20 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14421;
+
+/** @phpstan-impure */
+function get_optional_int(): ?int {
+	return random_int(0, 1) ? 42 : null;
+}
+
+if (isset($_SESSION['a'])) {
+    $b = $_SESSION['a'];
+}
+else {
+    $b = get_optional_int();
+}
+if ($b !== null) {
+ 	if (!isset($_SESSION['a'])) {
+		echo 'this is absolutely possible';
+	}
+}