diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index db31ce7669..8bdf7894e6 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -3956,7 +3956,9 @@ public function mergeWith(?self $otherScope): self
 
 			$expr = $expressionTypeHolder->getExpr();
 
-			return $expr instanceof Variable || $expr instanceof VirtualNode;
+			return $expr instanceof Variable
+				|| $expr instanceof FuncCall
+				|| $expr instanceof VirtualNode;
 		};
 
 		$mergedExpressionTypes = array_filter($mergedExpressionTypes, $filter);
diff --git a/tests/PHPStan/Rules/Comparison/NumberComparisonOperatorsConstantConditionRuleTest.php b/tests/PHPStan/Rules/Comparison/NumberComparisonOperatorsConstantConditionRuleTest.php
index 4c18f9e01e..818bed70ae 100644
--- a/tests/PHPStan/Rules/Comparison/NumberComparisonOperatorsConstantConditionRuleTest.php
+++ b/tests/PHPStan/Rules/Comparison/NumberComparisonOperatorsConstantConditionRuleTest.php
@@ -15,6 +15,8 @@ class NumberComparisonOperatorsConstantConditionRuleTest extends RuleTestCase
 
 	private bool $treatPhpDocTypesAsCertain = true;
 
+	private bool $polluteScopeWithAlwaysIterableForeach = true;
+
 	protected function getRule(): Rule
 	{
 		return new NumberComparisonOperatorsConstantConditionRule(
@@ -23,6 +25,11 @@ protected function getRule(): Rule
 		);
 	}
 
+	protected function shouldPolluteScopeWithAlwaysIterableForeach(): bool
+	{
+		return $this->polluteScopeWithAlwaysIterableForeach;
+	}
+
 	public function testBug8277(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-8277.php'], []);
@@ -269,6 +276,12 @@ public function testBug3387(): void
 		$this->analyse([__DIR__ . '/data/bug-3387.php'], []);
 	}
 
+	public function testBug13984(): void
+	{
+		$this->polluteScopeWithAlwaysIterableForeach = false;
+		$this->analyse([__DIR__ . '/data/bug-13984.php'], []);
+	}
+
 	public function testBug13874(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-13874.php'], []);
diff --git a/tests/PHPStan/Rules/Comparison/data/bug-13984.php b/tests/PHPStan/Rules/Comparison/data/bug-13984.php
new file mode 100644
index 0000000000..4c098c1e69
--- /dev/null
+++ b/tests/PHPStan/Rules/Comparison/data/bug-13984.php
@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace Bug13984;
+
+$list = [
+	'a',
+	'b',
+	'c',
+];
+
+/** @param list<string> $list */
+function acceptList(array $list): bool {
+	if (count($list) < 1) {
+		return false;
+	}
+
+	$compare = ['a', 'b', 'c'];
+
+	foreach($list as $key => $item) {
+		foreach ($compare as $k => $v) {
+			if ($item === $v && $v !== 'a') {
+				unset($list[$key]);
+			}
+		}
+	}
+
+	if (count($list) > 0) {
+		return true;
+	}
+
+	return false;
+}
+
+assert(acceptList($list) === true);