diff --git a/src/Type/ArrayType.php b/src/Type/ArrayType.php
index f6550a5845..13e7fafc52 100644
--- a/src/Type/ArrayType.php
+++ b/src/Type/ArrayType.php
@@ -410,6 +410,24 @@ public function setExistingOffsetValueType(Type $offsetType, Type $valueType): T
 			}
 		}
 
+		if (
+			$this->itemType->isArray()->yes()
+			&& $valueType->isArray()->yes()
+			&& $this->itemType->getIterableValueType()->isConstantArray()->yes()
+			&& $valueType->getIterableValueType()->isConstantArray()->yes()
+		) {
+			$newItemType = $this->itemType->setExistingOffsetValueType(
+				$valueType->getIterableKeyType(),
+				$valueType->getIterableValueType(),
+			);
+			if ($newItemType !== $this->itemType) {
+				return new self(
+					$this->keyType,
+					$newItemType,
+				);
+			}
+		}
+
 		return new self(
 			$this->keyType,
 			TypeCombinator::union($this->itemType, $valueType),
diff --git a/tests/PHPStan/Analyser/AnalyserIntegrationTest.php b/tests/PHPStan/Analyser/AnalyserIntegrationTest.php
index cf56a34adc..4a8a3d14a6 100644
--- a/tests/PHPStan/Analyser/AnalyserIntegrationTest.php
+++ b/tests/PHPStan/Analyser/AnalyserIntegrationTest.php
@@ -991,7 +991,7 @@ public function testBug7581(): void
 	public function testBug7903(): void
 	{
 		$errors = $this->runAnalyse(__DIR__ . '/data/bug-7903.php');
-		$this->assertCount(24, $errors);
+		$this->assertCount(23, $errors);
 	}
 
 	public function testBug7901(): void
diff --git a/tests/PHPStan/Analyser/nsrt/bug-13637.php b/tests/PHPStan/Analyser/nsrt/bug-13637.php
new file mode 100644
index 0000000000..4b9eed835d
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-13637.php
@@ -0,0 +1,43 @@
+<?php declare(strict_types = 1);
+
+namespace Bug13637;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @return array<int, array<int, array<int, array{abc: int, def: int, ghi: int}>>>
+ */
+function doesNotWork() : array {
+	$final = [];
+
+	for ($i = 0; $i < 5; $i++) {
+		$j = $i * 2;
+		$k = $j + 1;
+		$final[$i][$j][$k]['abc'] = $i;
+		$final[$i][$j][$k]['def'] = $i;
+		$final[$i][$j][$k]['ghi'] = $i;
+	}
+
+	assertType("non-empty-array<int<0, 4>, non-empty-array<int<0, 8>, non-empty-array<int<1, 9>, array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}>>>", $final);
+
+	return $final;
+}
+
+/**
+ * @return array<int, array<int, array{abc: int, def: int, ghi: int}>>
+ */
+function thisWorks() : array {
+	$final = [];
+
+	for ($i = 0; $i < 5; $i++) {
+		$j = $i * 2;
+		$k = $j + 1;
+		$final[$i][$j]['abc'] = $i;
+		$final[$i][$j]['def'] = $i;
+		$final[$i][$j]['ghi'] = $i;
+	}
+
+	assertType("non-empty-array<int<0, 4>, non-empty-array<int<0, 8>, array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}>>", $final);
+
+	return $final;
+}