diff --git a/src/Analyser/ExprHandler/AssignOpHandler.php b/src/Analyser/ExprHandler/AssignOpHandler.php
index ad3c1c67af..03669ecc0c 100644
--- a/src/Analyser/ExprHandler/AssignOpHandler.php
+++ b/src/Analyser/ExprHandler/AssignOpHandler.php
@@ -6,8 +6,6 @@
 use PhpParser\Node\Expr;
 use PhpParser\Node\Expr\AssignOp;
 use PhpParser\Node\Expr\BinaryOp;
-use PhpParser\Node\Expr\ConstFetch;
-use PhpParser\Node\Name;
 use PhpParser\Node\Stmt;
 use PHPStan\Analyser\AssignTargetWalkMode;
 use PHPStan\Analyser\ExpressionContext;
@@ -77,7 +75,7 @@ public function processExpr(NodeScopeResolver $nodeScopeResolver, Stmt $stmt, Ex
 		$valueContext = $context;
 		if ($expr instanceof Expr\AssignOp\Coalesce) {
 			$valueScope = $valueScope->filterByFalseyValue(
-				new BinaryOp\NotIdentical($expr->var, new ConstFetch(new Name('null'))),
+				new Expr\Isset_([$expr->var]),
 			);
 
 			if ($expr->var instanceof Expr\Variable && is_string($expr->var->name)) {
diff --git a/tests/PHPStan/Analyser/nsrt/bug-15021.php b/tests/PHPStan/Analyser/nsrt/bug-15021.php
new file mode 100644
index 0000000000..7864d1c5d2
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-15021.php
@@ -0,0 +1,185 @@
+<?php declare(strict_types = 1);
+
+namespace Bug15021;
+
+use function PHPStan\Testing\assertType;
+
+/** @param array{foo?: string, bar?: string} $data */
+function optionalOffset(array $data): void
+{
+	$data['foo'] ??= assertType('array{foo?: string, bar?: string}', $data);
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function optionalOffsetResult(array $data): void
+{
+	$data['foo'] ??= $data['bar'] ?? null;
+	assertType('array{foo: string|null, bar?: string}', $data);
+}
+
+/** @param array<string, string> $data */
+function nonConstantArray(array $data, string $key): void
+{
+	$data[$key] ??= assertType('array<string, string>', $data);
+}
+
+/** @param array<string, string> $data */
+function nonConstantArrayConstantKey(array $data): void
+{
+	$data['foo'] ??= assertType('array<string, string>', $data);
+}
+
+/** @param array<string, string|null> $data */
+function nonConstantArrayNullableValue(array $data): void
+{
+	$data['foo'] ??= assertType('string|null', $data['foo']);
+}
+
+/** @param array{a?: array{b?: string, c?: string}} $data */
+function nestedOptionalOffset(array $data): void
+{
+	$data['a']['b'] ??= assertType('array{a?: array{b?: string, c?: string}}', $data);
+}
+
+class Foo
+{
+
+	public string $nonNullable = '';
+
+	public static string $staticNonNullable = '';
+
+	/** @var array{foo?: string, bar?: string} */
+	public array $data = [];
+
+}
+
+function nonNullableProperty(Foo $foo): void
+{
+	$foo->nonNullable ??= assertType('string', $foo->nonNullable);
+}
+
+function nonNullableStaticProperty(): void
+{
+	Foo::$staticNonNullable ??= assertType('string', Foo::$staticNonNullable);
+}
+
+function propertyOffset(Foo $foo): void
+{
+	$foo->data['foo'] ??= assertType('array{foo?: string, bar?: string}', $foo->data);
+}
+
+/** @param \ArrayAccess<string, string> $a */
+function nonNullableOffsetAccess(\ArrayAccess $a): void
+{
+	$a['foo'] ??= assertType('string|null', $a['foo']);
+}
+
+/** @param \ArrayAccess<string, string> $a */
+function nonNullableOffsetAccessCoalesce(\ArrayAccess $a): void
+{
+	$x = $a['foo'] ?? assertType('string|null', $a['foo']);
+}
+
+/** @param \ArrayAccess<string, string> $a */
+function nonNullableOffsetAccessDifferentOffset(\ArrayAccess $a): void
+{
+	$a['foo'] ??= assertType('string|null', $a['bar']);
+}
+
+/** @param \ArrayAccess<string, string|null> $a */
+function nullableOffsetAccess(\ArrayAccess $a): void
+{
+	$a['foo'] ??= assertType('string|null', $a['foo']);
+}
+
+/** @param \ArrayAccess<string, string|null> $a */
+function nullableOffsetAccessCoalesce(\ArrayAccess $a): void
+{
+	$x = $a['foo'] ?? assertType('string|null', $a['foo']);
+}
+
+/** @param \ArrayObject<string, string> $data */
+function arrayObjectOffset(\ArrayObject $data): void
+{
+	$data['foo'] ??= assertType('string|null', $data['foo']);
+}
+
+/** @param \ArrayObject<string, string> $data */
+function arrayObjectOffsetCoalesce(\ArrayObject $data): void
+{
+	$x = $data['foo'] ?? assertType('string|null', $data['foo']);
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function issetOnRightSide(array $data): void
+{
+	$data['foo'] ??= isset($data['bar']) ? assertType('string', $data['bar']) : 'fallback';
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function emptyOnRightSide(array $data): void
+{
+	$data['foo'] ??= empty($data['bar']) ? 'fallback' : assertType('non-falsy-string', $data['bar']);
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function unsetTargetBeforeAssignOp(array $data): void
+{
+	unset($data['foo']);
+	$data['foo'] ??= assertType('array{bar?: string}', $data);
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function emptyTargetBeforeAssignOp(array $data): void
+{
+	if (empty($data['foo'])) {
+		$data['foo'] ??= assertType('array{foo?: string, bar?: string}', $data);
+	}
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function assignOpInsideEmpty(array $data): void
+{
+	if (empty($data['foo'] ??= assertType('array{foo?: string, bar?: string}', $data))) {
+		echo 'empty';
+	}
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function assignOpInsideIsset(array $data): void
+{
+	if (isset($data['foo'] ??= assertType('array{foo?: string, bar?: string}', $data))) {
+		echo 'isset';
+	}
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function assignOpInsideUnsetOffset(array $data): void
+{
+	$other = ['x' => 1, 'fallback' => 2];
+	unset($other[$data['foo'] ??= assertType('array{foo?: string, bar?: string}', $data)]);
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function assignOpResultInsideEmpty(array $data): void
+{
+	if (empty($data['foo'] ??= $data['bar'] ?? 'fallback')) {
+		assertType("array{foo: ''|'0', bar?: string}", $data);
+	}
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function assignOpResultInsideIsset(array $data): void
+{
+	if (isset($data['foo'] ??= $data['bar'] ?? null)) {
+		assertType('array{foo: string, bar?: string}', $data);
+	}
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function unsetAssignOpResultOffset(array $data): void
+{
+	$other = ['x' => 1, 'fallback' => 2];
+	unset($other[$data['foo'] ??= $data['bar'] ?? 'fallback']);
+	assertType('array{x?: 1, fallback?: 2}', $other);
+}
diff --git a/tests/PHPStan/Rules/Variables/EmptyRuleTest.php b/tests/PHPStan/Rules/Variables/EmptyRuleTest.php
index 079b032e8e..6ab498be10 100644
--- a/tests/PHPStan/Rules/Variables/EmptyRuleTest.php
+++ b/tests/PHPStan/Rules/Variables/EmptyRuleTest.php
@@ -250,4 +250,11 @@ public function testIssetAfterRememberedConstructor(): void
 		]);
 	}
 
+	public function testNullCoalesceAssignRightSideScope(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+
+		$this->analyse([__DIR__ . '/data/null-coalesce-assign-right-side-scope.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Variables/IssetRuleTest.php b/tests/PHPStan/Rules/Variables/IssetRuleTest.php
index af8f1542e0..db77f2aef5 100644
--- a/tests/PHPStan/Rules/Variables/IssetRuleTest.php
+++ b/tests/PHPStan/Rules/Variables/IssetRuleTest.php
@@ -610,4 +610,11 @@ public function testBug14610(): void
 		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-14610.php'], []);
 	}
 
+	public function testNullCoalesceAssignRightSideScope(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+
+		$this->analyse([__DIR__ . '/data/null-coalesce-assign-right-side-scope.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php b/tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php
index 17d1dd8594..4c39265508 100644
--- a/tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php
+++ b/tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php
@@ -558,4 +558,43 @@ public function testBug14393(): void
 		]);
 	}
 
+	public function testBug15021(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-15021.php'], []);
+	}
+
+	public function testNullCoalesceAssignRightSideScope(): void
+	{
+		$this->analyse([__DIR__ . '/data/null-coalesce-assign-right-side-scope.php'], [
+			[
+				'Property NullCoalesceAssignRightSideScope\Foo::$nonNullable (string) on left side of ??= is not nullable.',
+				19,
+			],
+			[
+				'Property NullCoalesceAssignRightSideScope\Foo::$nonNullable (string) on left side of ?? is not nullable.',
+				19,
+			],
+			[
+				'Static property NullCoalesceAssignRightSideScope\Foo::$staticNonNullable (string) on left side of ??= is not nullable.',
+				24,
+			],
+			[
+				'Static property NullCoalesceAssignRightSideScope\Foo::$staticNonNullable (string) on left side of ?? is not nullable.',
+				24,
+			],
+			[
+				'Variable $undefined on left side of ??= is never defined.',
+				46,
+			],
+			[
+				'Variable $undefined on left side of ?? is never defined.',
+				46,
+			],
+			[
+				'Offset \'foo\' on array{bar?: string} on left side of ??= does not exist.',
+				89,
+			],
+		]);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Variables/UnsetRuleTest.php b/tests/PHPStan/Rules/Variables/UnsetRuleTest.php
index 3bef8ab900..73515e60d5 100644
--- a/tests/PHPStan/Rules/Variables/UnsetRuleTest.php
+++ b/tests/PHPStan/Rules/Variables/UnsetRuleTest.php
@@ -224,4 +224,9 @@ public function testUnsetHookedProperty(): void
 		]);
 	}
 
+	public function testNullCoalesceAssignRightSideScope(): void
+	{
+		$this->analyse([__DIR__ . '/data/null-coalesce-assign-right-side-scope.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Variables/data/bug-15021.php b/tests/PHPStan/Rules/Variables/data/bug-15021.php
new file mode 100644
index 0000000000..9d23d7734a
--- /dev/null
+++ b/tests/PHPStan/Rules/Variables/data/bug-15021.php
@@ -0,0 +1,8 @@
+<?php declare(strict_types = 1);
+
+namespace Bug15021;
+
+/** @param array{foo?: string, bar?: string} $data */
+function foo(array $data): void {
+	$data['foo'] ??= $data['bar'] ?? null;
+}
diff --git a/tests/PHPStan/Rules/Variables/data/null-coalesce-assign-right-side-scope.php b/tests/PHPStan/Rules/Variables/data/null-coalesce-assign-right-side-scope.php
new file mode 100644
index 0000000000..9f4d6b214f
--- /dev/null
+++ b/tests/PHPStan/Rules/Variables/data/null-coalesce-assign-right-side-scope.php
@@ -0,0 +1,113 @@
+<?php declare(strict_types = 1);
+
+namespace NullCoalesceAssignRightSideScope;
+
+final class Foo
+{
+
+	public string $nonNullable = '';
+
+	public static string $staticNonNullable = '';
+
+	/** @var array{foo?: string, bar?: string} */
+	public array $data = [];
+
+}
+
+function property(Foo $foo): void
+{
+	$foo->nonNullable ??= $foo->nonNullable ?? null;
+}
+
+function staticProperty(): void
+{
+	Foo::$staticNonNullable ??= Foo::$staticNonNullable ?? null;
+}
+
+function propertyOffset(Foo $foo): void
+{
+	$foo->data['foo'] ??= $foo->data['bar'] ?? null;
+}
+
+/** @param array{a?: array{b?: string, c?: string}} $data */
+function nestedOffset(array $data): void
+{
+	$data['a']['b'] ??= $data['a']['c'] ?? null;
+}
+
+/** @param array<string, string> $data */
+function nonConstantArray(array $data, string $key): void
+{
+	$data[$key] ??= $data['fallback'] ?? null;
+}
+
+function undefinedVariable(): void
+{
+	$undefined ??= $undefined ?? 1;
+}
+
+/** @param \ArrayAccess<string, string> $a */
+function nonNullableOffsetAccess(\ArrayAccess $a): void
+{
+	$a['foo'] ??= $a['foo'] ?? null;
+}
+
+/** @param \ArrayAccess<string, string> $a */
+function nonNullableOffsetAccessDifferentOffset(\ArrayAccess $a): void
+{
+	$a['foo'] ??= $a['bar'] ?? null;
+}
+
+/** @param \ArrayAccess<string, string|null> $a */
+function nullableOffsetAccess(\ArrayAccess $a): void
+{
+	$a['foo'] ??= $a['foo'] ?? null;
+}
+
+/** @param \ArrayObject<string, string> $data */
+function arrayObjectOffset(\ArrayObject $data): void
+{
+	$data['foo'] ??= $data['foo'] ?? null;
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function issetOnRightSide(array $data): void
+{
+	$data['foo'] ??= isset($data['bar']) ? $data['bar'] : 'fallback';
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function emptyOnRightSide(array $data): void
+{
+	$data['foo'] ??= empty($data['bar']) ? 'fallback' : $data['bar'];
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function unsetTargetBeforeAssignOp(array $data): void
+{
+	unset($data['foo']);
+	$data['foo'] ??= $data['bar'] ?? null;
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function emptyTargetBeforeAssignOp(array $data): void
+{
+	if (empty($data['foo'])) {
+		$data['foo'] ??= $data['bar'] ?? null;
+	}
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function assignOpInsideEmpty(array $data): void
+{
+	if (empty($data['foo'] ??= $data['bar'] ?? null)) {
+		echo 'empty';
+	}
+}
+
+/** @param array{foo?: string, bar?: string} $data */
+function assignOpInsideUnsetOffset(array $data): void
+{
+	$other = ['x' => 1, 'fallback' => 2];
+	unset($other[$data['foo'] ??= $data['bar'] ?? 'fallback']);
+}