diff --git a/src/Analyser/ExprHandler/Helper/ConditionalExpressionHolderHelper.php b/src/Analyser/ExprHandler/Helper/ConditionalExpressionHolderHelper.php
index e8c1008c183..a59f29cd6d6 100644
--- a/src/Analyser/ExprHandler/Helper/ConditionalExpressionHolderHelper.php
+++ b/src/Analyser/ExprHandler/Helper/ConditionalExpressionHolderHelper.php
@@ -17,7 +17,6 @@
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Type\NeverType;
 use PHPStan\Type\TypeCombinator;
-use function array_keys;
 use function count;
 use function is_string;
 
@@ -201,10 +200,12 @@ public function processBooleanConditionalTypes(Scope $scope, SpecifiedTypes $con
 				}
 
 				$conditions = $conditionExpressionTypes;
-				foreach (array_keys($conditions) as $conditionExprString) {
+				$droppedSelfCondition = null;
+				foreach ($conditions as $conditionExprString => $condition) {
 					if ($conditionExprString !== $exprString) {
 						continue;
 					}
+					$droppedSelfCondition = $condition;
 					unset($conditions[$conditionExprString]);
 				}
 
@@ -218,6 +219,16 @@ public function processBooleanConditionalTypes(Scope $scope, SpecifiedTypes $con
 					? TypeCombinator::intersect($targetType, $type)
 					: TypeCombinator::remove($targetType, $type);
 
+				// The dropped self-condition narrowed the target; without it the
+				// holder must allow the values it excluded, or it over-narrows when
+				// only the remaining conditions hold. So union back the complement.
+				if ($droppedSelfCondition !== null) {
+					$complement = TypeCombinator::remove($scope->getType($expr), $droppedSelfCondition->getType());
+					if (!$complement instanceof NeverType) {
+						$holderType = TypeCombinator::union($holderType, $complement);
+					}
+				}
+
 				// These boolean-decomposition holders only refine an expression's
 				// type in a future scope; they must never collapse it to never and
 				// thereby mark the whole scope unreachable. A never result is an
diff --git a/tests/PHPStan/Analyser/nsrt/bug-14874.php b/tests/PHPStan/Analyser/nsrt/bug-14874.php
new file mode 100644
index 00000000000..28506ef3e38
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-14874.php
@@ -0,0 +1,29 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14874;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param array<mixed> $a
+ */
+function test(array $a): bool {
+	if (isset($a['foo']) && !is_array($a['foo']))
+		return false;
+	if (array_key_exists('foo', $a)) {
+		assertType('array<mixed, mixed>|null', $a['foo']);
+		return $a['foo'] === null; // possible
+	}
+	return false;
+}
+
+/**
+ * @param array<mixed> $a
+ */
+function testIs(array $a): void {
+	if (isset($a['foo']) && !is_int($a['foo']))
+		return;
+	if (array_key_exists('foo', $a)) {
+		assertType('int|null', $a['foo']);
+	}
+}