diff --git a/src/Type/ArrayType.php b/src/Type/ArrayType.php
index 288caefdc6..d0c85461ed 100644
--- a/src/Type/ArrayType.php
+++ b/src/Type/ArrayType.php
@@ -408,6 +408,24 @@ public function setExistingOffsetValueType(Type $offsetType, Type $valueType): T
 					$newItemType,
 				);
 			}
+		} elseif (
+			$this->itemType->isArray()->yes()
+			&& !$this->itemType->isConstantArray()->yes()
+			&& $valueType->isArray()->yes()
+			&& !$valueType->isConstantArray()->yes()
+			&& $this->itemType->getIterableValueType()->isArray()->yes()
+			&& $valueType->getIterableValueType()->isArray()->yes()
+		) {
+			$newItemType = $this->itemType->setExistingOffsetValueType(
+				$valueType->getIterableKeyType(),
+				$valueType->getIterableValueType(),
+			);
+			if ($newItemType !== $this->itemType) {
+				return new self(
+					$this->keyType,
+					$newItemType,
+				);
+			}
 		}
 
 		return new self(
diff --git a/tests/PHPStan/Analyser/nsrt/bug-13637.php b/tests/PHPStan/Analyser/nsrt/bug-13637.php
new file mode 100644
index 0000000000..fe374bb1af
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-13637.php
@@ -0,0 +1,136 @@
+<?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;
+		$l = $i * 3;
+		$final[$i][$j][$k]['abc'] = $i;
+		$final[$i][$j][$k]['def'] = $i;
+		$final[$i][$j][$k]['ghi'] = $i;
+
+		assertType("array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}", $final[$i][$j][$k]);
+		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);
+	}
+
+	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<int, array<int, array{abc: int, def: int, ghi: int}>>>>
+*/
+function fourLevelsDeep() : array {
+	$final = [];
+
+	for ($i = 0; $i < 5; $i++) {
+		$j = $i * 2;
+		$k = $j + 1;
+		$l = $i * 3;
+		$final[$i][$j][$k][$l]['abc'] = $i;
+		$final[$i][$j][$k][$l]['def'] = $i;
+		$final[$i][$j][$k][$l]['ghi'] = $i;
+
+		assertType("array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}", $final[$i][$j][$k][$l]);
+		assertType("non-empty-array<int<0, 4>, non-empty-array<int<0, 8>, non-empty-array<int<1, 9>, non-empty-array<int<0, 12>, array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}>>>>", $final);
+	}
+
+	assertType("non-empty-array<int<0, 4>, non-empty-array<int<0, 8>, non-empty-array<int<1, 9>, non-empty-array<int<0, 12>, array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}>>>>", $final);
+	return $final;
+}
+
+/**
+* @return array<int, array<int, array<int, array<int, array<int, array{abc: int, def: int, ghi: int}>>>>>
+*/
+function fiveLevelsDeep() : array {
+	$final = [];
+
+	for ($i = 0; $i < 5; $i++) {
+		$j = $i * 2;
+		$k = $j + 1;
+		$l = $i * 3;
+		$m = $i + 10;
+		$final[$i][$j][$k][$l][$m]['abc'] = $i;
+		$final[$i][$j][$k][$l][$m]['def'] = $i;
+		$final[$i][$j][$k][$l][$m]['ghi'] = $i;
+
+		assertType("array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}", $final[$i][$j][$k][$l][$m]);
+		assertType("non-empty-array<int<0, 4>, non-empty-array<int<0, 8>, non-empty-array<int<1, 9>, non-empty-array<int<0, 12>, non-empty-array<int<10, 14>, array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}>>>>>", $final);
+	}
+
+	assertType("non-empty-array<int<0, 4>, non-empty-array<int<0, 8>, non-empty-array<int<1, 9>, non-empty-array<int<0, 12>, non-empty-array<int<10, 14>, array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}>>>>>", $final);
+	return $final;
+}
+
+/**
+* @return array<int, array<int, array<int, array<int, array<int, array<int, array{abc: int, def: int, ghi: int}>>>>>>
+*/
+function sixLevelsDeep() : array {
+	$final = [];
+
+	for ($i = 0; $i < 5; $i++) {
+		$j = $i * 2;
+		$k = $j + 1;
+		$l = $i * 3;
+		$m = $i + 10;
+		$n = $i + 20;
+		$final[$i][$j][$k][$l][$m][$n]['abc'] = $i;
+		$final[$i][$j][$k][$l][$m][$n]['def'] = $i;
+		$final[$i][$j][$k][$l][$m][$n]['ghi'] = $i;
+
+		assertType("array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}", $final[$i][$j][$k][$l][$m][$n]);
+		assertType("non-empty-array<int<0, 4>, non-empty-array<int<0, 8>, non-empty-array<int<1, 9>, non-empty-array<int<0, 12>, non-empty-array<int<10, 14>, non-empty-array<int<20, 24>, array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}>>>>>>", $final);
+	}
+
+	assertType("non-empty-array<int<0, 4>, non-empty-array<int<0, 8>, non-empty-array<int<1, 9>, non-empty-array<int<0, 12>, non-empty-array<int<10, 14>, non-empty-array<int<20, 24>, array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}>>>>>>", $final);
+	return $final;
+}
+
+/** Tests that maybe-array item type (union with non-array) skips the recursive path */
+function maybeArrayItemType(bool $flag): void {
+	$final = [];
+
+	for ($i = 0; $i < 5; $i++) {
+		$j = $i * 2;
+		$k = $j + 1;
+		if ($flag) {
+			$final[$i][$j][$k]['abc'] = $i;
+			$final[$i][$j][$k]['def'] = $i;
+		} else {
+			$final[$i] = $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>}>>|int<0, 4>>", $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;
+		$l = $i * 3;
+		$final[$i][$j]['abc'] = $i;
+		$final[$i][$j]['def'] = $i;
+		$final[$i][$j]['ghi'] = $i;
+
+		assertType("array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}", $final[$i][$j]);
+		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);
+	}
+
+	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;
+}