diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index 122340cc27..39e8c4bfaf 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -3279,6 +3279,51 @@ public function filterBySpecifiedTypes(SpecifiedTypes $specifiedTypes): self
 			}
 		}
 
+		// Update stored FuncCall expression types whose arguments were narrowed.
+		// The stored type may be stale (from scope merging) while the argument
+		// types have been freshly narrowed. Intersect with the dynamically
+		// computed type so both sources of narrowing are preserved.
+		$funcCallsToUpdate = [];
+		foreach ($scope->expressionTypes as $exprString => $exprTypeHolder) {
+			if (array_key_exists($exprString, $specifiedExpressions) || array_key_exists($exprString, $conditions)) {
+				continue;
+			}
+			$expr = $exprTypeHolder->getExpr();
+			if (!$expr instanceof FuncCall) {
+				continue;
+			}
+			foreach ($expr->getArgs() as $arg) {
+				$argKey = $this->getNodeKey($arg->value);
+				if (!array_key_exists($argKey, $specifiedExpressions)) {
+					continue;
+				}
+				$oldArgType = array_key_exists($argKey, $this->expressionTypes)
+					? $this->expressionTypes[$argKey]->getType()
+					: null;
+				$newArgType = array_key_exists($argKey, $scope->expressionTypes)
+					? $scope->expressionTypes[$argKey]->getType()
+					: null;
+				if ($oldArgType !== null && $newArgType !== null && $oldArgType->equals($newArgType)) {
+					continue;
+				}
+				$funcCallsToUpdate[$exprString] = $exprTypeHolder;
+				break;
+			}
+		}
+
+		foreach ($funcCallsToUpdate as $exprString => $exprTypeHolder) {
+			$storedType = $exprTypeHolder->getType();
+			unset($scope->expressionTypes[$exprString]);
+			unset($scope->nativeExpressionTypes[$exprString]);
+			unset($scope->resolvedTypes[$exprString]);
+			$dynamicType = $scope->getType($exprTypeHolder->getExpr());
+			$scope->expressionTypes[$exprString] = new ExpressionTypeHolder(
+				$exprTypeHolder->getExpr(),
+				TypeCombinator::intersect($storedType, $dynamicType),
+				$exprTypeHolder->getCertainty(),
+			);
+		}
+
 		return $scope->scopeFactory->create(
 			$scope->context,
 			$scope->isDeclareStrictTypes(),
diff --git a/tests/PHPStan/Analyser/nsrt/bug-13750.php b/tests/PHPStan/Analyser/nsrt/bug-13750.php
new file mode 100644
index 0000000000..30dc1a96cd
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-13750.php
@@ -0,0 +1,52 @@
+<?php
+
+namespace Bug13750;
+
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+	/** @param array<mixed> $arr */
+	public function forgetCount(array $arr): void
+	{
+		if (count($arr) > 2) {
+			assertType('non-empty-array<mixed>', $arr);
+			assertType('int<3, max>', count($arr));
+		}
+		assertType('array<mixed>', $arr);
+		assertType('int<0, max>', count($arr));
+		if (count($arr, COUNT_RECURSIVE) > 2) {
+			assertType('non-empty-array<mixed>', $arr);
+			assertType('int<1, max>', count($arr));
+		}
+	}
+
+	/** @param array<mixed> $arr */
+	public function forgetCountDifferentNarrowing(array $arr): void
+	{
+		if (count($arr) > 2) {
+		}
+		if ($arr !== []) {
+			assertType('int<1, max>', count($arr));
+		}
+	}
+
+	/** @param array<mixed> $arr */
+	public function sizeofAfterSizeof(array $arr): void
+	{
+		if (sizeof($arr) > 2) {
+		}
+		if ($arr !== []) {
+			assertType('int<1, max>', sizeof($arr));
+		}
+	}
+
+	public function strlenAfterStrlen(string $str): void
+	{
+		if (strlen($str) > 5) {
+		}
+		if ($str !== '') {
+			assertType('int<1, max>', strlen($str));
+		}
+	}
+}