diff --git a/tests/PHPStan/Rules/Variables/DefinedVariableRuleTest.php b/tests/PHPStan/Rules/Variables/DefinedVariableRuleTest.php
index 207070c762..6da8dfb7a5 100644
--- a/tests/PHPStan/Rules/Variables/DefinedVariableRuleTest.php
+++ b/tests/PHPStan/Rules/Variables/DefinedVariableRuleTest.php
@@ -1517,4 +1517,18 @@ public function testBug11218(): void
 		$this->analyse([__DIR__ . '/data/bug-11218.php'], []);
 	}
 
+	public function testBug6688(): void
+	{
+		$this->cliArgumentsVariablesRegistered = true;
+		$this->polluteScopeWithLoopInitialAssignments = false;
+		$this->checkMaybeUndefinedVariables = true;
+		$this->polluteScopeWithAlwaysIterableForeach = true;
+		$this->analyse([__DIR__ . '/data/bug-6688.php'], [
+			[
+				'Variable $a might not be defined.',
+				5,
+			],
+		]);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Variables/data/bug-6688.php b/tests/PHPStan/Rules/Variables/data/bug-6688.php
new file mode 100644
index 0000000000..c1c98925c2
--- /dev/null
+++ b/tests/PHPStan/Rules/Variables/data/bug-6688.php
@@ -0,0 +1,17 @@
+<?php declare(strict_types = 1);
+
+namespace Bug6688;
+
+echo $a; // possibly undefined
+
+/** @var string $b */
+echo $b; // willed into existence
+
+/** @var string[] $c */
+foreach ($c as $v) { // willed into existence
+}
+
+/** @var string[][] $result */
+foreach ($result as $data) {
+	echo '"' . implode('", "', $data) . '"' . "\n";
+}