diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index d98c716fe1..bbd489a844 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -4100,6 +4100,8 @@ public function unsetExpression(Expr $expr): self
 				$this->getType($expr->var)->unsetOffset($this->getType($expr->dim)),
 			)->invalidateExpression(
 				new FuncCall(new FullyQualified('count'), [new Arg($expr->var)]),
+			)->invalidateExpression(
+				new FuncCall(new FullyQualified('sizeof'), [new Arg($expr->var)]),
 			);
 		}
 
diff --git a/tests/PHPStan/Analyser/NodeScopeResolverTest.php b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
index 4c236f85be..088619e961 100644
--- a/tests/PHPStan/Analyser/NodeScopeResolverTest.php
+++ b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
@@ -702,6 +702,8 @@ public function dataFileAsserts(): iterable
 		}
 
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6500.php');
+
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6488.php');
 	}
 
 	/**
diff --git a/tests/PHPStan/Analyser/data/bug-6488.php b/tests/PHPStan/Analyser/data/bug-6488.php
new file mode 100644
index 0000000000..7f66763d2d
--- /dev/null
+++ b/tests/PHPStan/Analyser/data/bug-6488.php
@@ -0,0 +1,26 @@
+<?php
+
+namespace Bug6488;
+
+use function PHPStan\Testing\assertType;
+
+function test() {
+	$items = array_fill(0, rand(0, 5), rand(0, 100));
+
+
+	if (sizeof($items) === 0) {
+		return false;
+	}
+
+	if (sizeof($items) === 1) {
+		return false;
+	}
+
+	foreach ($items as $key => $value) {
+		if ($value % 2 === 0) {
+			unset($items[$key]);
+		}
+	}
+
+	assertType('bool',sizeof($items) > 0);
+}