diff --git a/src/Type/IntersectionType.php b/src/Type/IntersectionType.php
index 851fb49a8b..e85ee03dc6 100644
--- a/src/Type/IntersectionType.php
+++ b/src/Type/IntersectionType.php
@@ -56,6 +56,10 @@ public function accepts(Type $otherType, bool $strictTypes): TrinaryLogic
 
 	public function isSuperTypeOf(Type $otherType): TrinaryLogic
 	{
+		if ($otherType instanceof IntersectionType && $this->equals($otherType)) {
+			return TrinaryLogic::createYes();
+		}
+
 		$results = [];
 		foreach ($this->getTypes() as $innerType) {
 			$results[] = $innerType->isSuperTypeOf($otherType);
diff --git a/tests/PHPStan/Analyser/AnalyserIntegrationTest.php b/tests/PHPStan/Analyser/AnalyserIntegrationTest.php
index 33da205b75..3664a347ed 100644
--- a/tests/PHPStan/Analyser/AnalyserIntegrationTest.php
+++ b/tests/PHPStan/Analyser/AnalyserIntegrationTest.php
@@ -256,6 +256,12 @@ public function testBug3468(): void
 		$this->assertCount(0, $errors);
 	}
 
+	public function testBug3686(): void
+	{
+		$errors = $this->runAnalyse(__DIR__ . '/data/bug-3686.php');
+		$this->assertCount(0, $errors);
+	}
+
 	/**
 	 * @param string $file
 	 * @return \PHPStan\Analyser\Error[]
diff --git a/tests/PHPStan/Analyser/data/bug-3686.php b/tests/PHPStan/Analyser/data/bug-3686.php
new file mode 100644
index 0000000000..586a62a771
--- /dev/null
+++ b/tests/PHPStan/Analyser/data/bug-3686.php
@@ -0,0 +1,39 @@
+<?php
+
+namespace Bug3686;
+
+/**
+ * @param mixed $request
+ * @return void
+ */
+function fred($request)
+{
+	$keys = '';
+	foreach ($request as $index)
+	{
+		foreach ($index as $field)
+		{
+			if (isset($keys[$field]))
+			{
+				$keys[$field] = 0;
+			}
+		}
+	}
+}
+
+/**
+ * @param int[][] $a
+ */
+function replaceStringWithZero(array $a) : string {
+	$keys = 'agfsdafsafdrew1231414';
+
+	foreach ($a as $b) {
+		foreach ($b as $c) {
+			if (isset($keys[$c])) {
+				$keys[$c] = "0";
+			}
+		}
+	}
+
+	return $keys;
+}
diff --git a/tests/PHPStan/Type/TypeCombinatorTest.php b/tests/PHPStan/Type/TypeCombinatorTest.php
index d09a69f6f3..095eca9963 100644
--- a/tests/PHPStan/Type/TypeCombinatorTest.php
+++ b/tests/PHPStan/Type/TypeCombinatorTest.php
@@ -1679,6 +1679,22 @@ public function dataUnion(): array
 				UnionType::class,
 				'array(\'a\' => int, \'b\' => int)|array(\'b\' => int, \'c\' => int)',
 			],
+			[
+				[
+					TypeCombinator::intersect(new StringType(), new HasOffsetType(new IntegerType())),
+					TypeCombinator::intersect(new StringType(), new HasOffsetType(new IntegerType())),
+				],
+				IntersectionType::class,
+				'string&hasOffset(int)',
+			],
+			[
+				[
+					TypeCombinator::intersect(new ConstantStringType('abc'), new HasOffsetType(new IntegerType())),
+					TypeCombinator::intersect(new ConstantStringType('abc'), new HasOffsetType(new IntegerType())),
+				],
+				IntersectionType::class,
+				'\'abc\'&hasOffset(int)',
+			],
 		];
 	}
 
@@ -2734,6 +2750,14 @@ public function dataIntersect(): array
 				ConstantArrayType::class,
 				'array(\'a\' => int, \'b\' => int)',
 			],
+			[
+				[
+					new StringType(),
+					new HasOffsetType(new IntegerType()),
+				],
+				IntersectionType::class,
+				'string&hasOffset(int)',
+			],
 		];
 	}