diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index a26a86a066..48f592e4c5 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -3833,7 +3833,15 @@ public function filterBySpecifiedTypes(SpecifiedTypes $specifiedTypes): self
 					}
 
 					$conditions[$conditionalExprString][] = $conditionalExpression;
-					$specifiedExpressions[$conditionalExprString] = $conditionalExpression->getTypeHolder();
+					$newTypeHolder = $conditionalExpression->getTypeHolder();
+					if (array_key_exists($conditionalExprString, $specifiedExpressions) && $specifiedExpressions[$conditionalExprString]->getCertainty()->yes() && $newTypeHolder->getCertainty()->yes()) {
+						$specifiedExpressions[$conditionalExprString] = ExpressionTypeHolder::createYes(
+							$newTypeHolder->getExpr(),
+							TypeCombinator::intersect($specifiedExpressions[$conditionalExprString]->getType(), $newTypeHolder->getType()),
+						);
+					} else {
+						$specifiedExpressions[$conditionalExprString] = $newTypeHolder;
+					}
 				}
 			}
 		}
diff --git a/tests/PHPStan/Analyser/nsrt/bug-14211.php b/tests/PHPStan/Analyser/nsrt/bug-14211.php
new file mode 100644
index 0000000000..8effe5a25a
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-14211.php
@@ -0,0 +1,25 @@
+<?php declare(strict_types=1);
+
+namespace Bug14211;
+
+use function PHPStan\Testing\assertType;
+
+/** @param array<mixed> $data */
+function doSomething(array $data): bool {
+
+	if (!isset($data['x']))
+		return false;
+
+	$m = isset($data['y']);
+
+	if ($m) {
+		assertType('true', $m);
+	}
+	assertType('bool', $m);
+
+	if ($m) {
+		assertType('true', $m);
+	}
+
+	return true;
+}