diff --git a/src/Analyser/ExprHandler/AssignHandler.php b/src/Analyser/ExprHandler/AssignHandler.php
index 0a1f5f83e84..d9c45d8064a 100644
--- a/src/Analyser/ExprHandler/AssignHandler.php
+++ b/src/Analyser/ExprHandler/AssignHandler.php
@@ -2156,6 +2156,13 @@ private function currentTypeForConditionalHolder(NodeScopeResolver $nodeScopeRes
 		// (@phpstan-assert property fetches etc.) answer from scope state or a walk
 		$storedResult = $storage->findExpressionResult($expr);
 		if ($storedResult !== null) {
+			// a subexpression walked on a narrower branch (the right side of
+			// `$a['k'] === null || is_int($a['k'])` sees `$a['k']` without null)
+			// does not answer on this scope - re-price it here
+			if (!$storedResult->answersOnScope($scope, $scope->nativeTypesPromoted)) {
+				return $nodeScopeResolver->processExprOnDemand($expr, $scope, new ExpressionResultStorage())->getTypeOnScope($scope, $scope->nativeTypesPromoted);
+			}
+
 			return $storedResult->getTypeOnScope($scope, $scope->nativeTypesPromoted);
 		}
 
diff --git a/src/Turbo/TurboExtensionEnabler.php b/src/Turbo/TurboExtensionEnabler.php
index 374d29043e6..1c3cb2e5662 100644
--- a/src/Turbo/TurboExtensionEnabler.php
+++ b/src/Turbo/TurboExtensionEnabler.php
@@ -33,7 +33,7 @@
 final class TurboExtensionEnabler
 {
 
-	public const EXPECTED_EXTENSION_VERSION = 'a0f7086';
+	public const EXPECTED_EXTENSION_VERSION = '7bcf6c4';
 
 	private static bool $active = false;
 
diff --git a/tests/PHPStan/Analyser/nsrt/bug-15479.php b/tests/PHPStan/Analyser/nsrt/bug-15479.php
new file mode 100644
index 00000000000..a9dc81a7f02
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-15479.php
@@ -0,0 +1,26 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug15479;
+
+use function PHPStan\Testing\assertType;
+
+/** @param array<string, mixed> $a */
+function f(array $a): void {
+    $ok = array_key_exists('k', $a) && ($a['k'] === null || is_int($a['k']));
+    if ($ok) { assertType('int|null', $a['k']); }
+}
+/** @param array<string, mixed> $a */
+function g(array $a): void {
+    $ok = ($a['k'] === null || is_int($a['k']));
+    if ($ok) { assertType('int|null', $a['k']); }
+}
+/** @param array<string, mixed> $a */
+function h(array $a): void {
+    if (array_key_exists('k', $a) && ($a['k'] === null || is_int($a['k']))) { assertType('int|null', $a['k']); }
+}
+function i(mixed $v): void {
+    $ok = $v === null || is_int($v);
+    if ($ok) { assertType('int|null', $v); }
+}
diff --git a/turbo-ext/src/AssignHandler.cpp b/turbo-ext/src/AssignHandler.cpp
index f5a81e3b4bc..95ebcf41251 100644
--- a/turbo-ext/src/AssignHandler.cpp
+++ b/turbo-ext/src/AssignHandler.cpp
@@ -2447,7 +2447,22 @@ class AssignHandler
 		// on loop-convergence passes); synthetic terms narrowing extensions built
 		// (@phpstan-assert property fetches etc.) answer from scope state or a walk
 		AH_VAL(storedResult, pt_expression_result_storage_find(storage, expr));
-		if (!storedResult.isNull()) return ahTypeOnScope(storedResult.raw(), scope);
+		if (!storedResult.isNull()) {
+			// a subexpression walked on a narrower branch (the right side of
+			// `$a['k'] === null || is_int($a['k'])` sees `$a['k']` without null)
+			// does not answer on this scope - re-price it here
+			bool promoted;
+			AH_OK(ahPromoted(scope, promoted));
+			bool answers;
+			AH_OK(pt_expression_result_answers_on_scope(storedResult.raw(), scope, promoted, answers));
+			if (!answers) {
+				AH_VAL(onDemandStorage, pt_expression_result_storage_new());
+				AH_VAL(onDemandResult, pt_node_scope_resolver_process_expr_on_demand(nsr, expr, scope, onDemandStorage.raw()));
+				return ahTypeOnScope(onDemandResult.raw(), scope);
+			}
+
+			return ahTypeOnScope(storedResult.raw(), scope);
+		}
 
 		return nsrReadScopeStateOrSyntheticType(nsr, expr, scope);
 	}