diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index c9d9f6339f0..691b77ec5a0 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -2023,18 +2023,7 @@ public function enterAnonymousFunctionWithoutReflection(
 			$isNullable = $this->isParameterValueNullable($parameter);
 			$parameterType = $this->getFunctionType($parameter->type, $isNullable, $parameter->variadic);
 			if ($callableParameters !== null) {
-				if (isset($callableParameters[$i])) {
-					$parameterType = self::intersectButNotNever($parameterType, $callableParameters[$i]->getType());
-				} elseif (count($callableParameters) > 0) {
-					$lastParameter = array_last($callableParameters);
-					if ($lastParameter->isVariadic()) {
-						$parameterType = self::intersectButNotNever($parameterType, $lastParameter->getType());
-					} else {
-						$parameterType = self::intersectButNotNever($parameterType, new MixedType());
-					}
-				} else {
-					$parameterType = self::intersectButNotNever($parameterType, new MixedType());
-				}
+				$parameterType = self::intersectButNotNever($parameterType, $this->getCallableParameterType($callableParameters, $i));
 			}
 			$holder = ExpressionTypeHolder::createYes($parameter->var, $parameterType);
 			$expressionTypes[$paramExprString] = $holder;
@@ -2233,20 +2222,8 @@ public function enterArrowFunctionWithoutReflection(Expr\ArrowFunction $arrowFun
 		foreach ($arrowFunction->params as $i => $parameter) {
 			$isNullable = $this->isParameterValueNullable($parameter);
 			$parameterType = $this->getFunctionType($parameter->type, $isNullable, $parameter->variadic);
-
 			if ($callableParameters !== null) {
-				if (isset($callableParameters[$i])) {
-					$parameterType = self::intersectButNotNever($parameterType, $callableParameters[$i]->getType());
-				} elseif (count($callableParameters) > 0) {
-					$lastParameter = array_last($callableParameters);
-					if ($lastParameter->isVariadic()) {
-						$parameterType = self::intersectButNotNever($parameterType, $lastParameter->getType());
-					} else {
-						$parameterType = self::intersectButNotNever($parameterType, new MixedType());
-					}
-				} else {
-					$parameterType = self::intersectButNotNever($parameterType, new MixedType());
-				}
+				$parameterType = self::intersectButNotNever($parameterType, $this->getCallableParameterType($callableParameters, $i));
 			}
 
 			if (!$parameter->var instanceof Variable || !is_string($parameter->var->name)) {
@@ -2312,6 +2289,27 @@ public function getFunctionType($type, bool $isNullable, bool $isVariadic): Type
 		return $this->initializerExprTypeResolver->getFunctionType($type, $isNullable, false, InitializerExprContext::fromScope($this));
 	}
 
+	/**
+	 * @param ParameterReflection[] $callableParameters
+	 */
+	private function getCallableParameterType(array $callableParameters, int $index): Type
+	{
+		if (isset($callableParameters[$index])) {
+			return $callableParameters[$index]->getType();
+		}
+
+		if (count($callableParameters) === 0) {
+			return new MixedType();
+		}
+
+		$lastParameter = array_last($callableParameters);
+		if ($lastParameter->isVariadic()) {
+			return $lastParameter->getType();
+		}
+
+		return new MixedType();
+	}
+
 	public static function intersectButNotNever(Type $nativeType, Type $inferredType): Type
 	{
 		if ($nativeType->isSuperTypeOf($inferredType)->no()) {
diff --git a/src/Type/ConditionalType.php b/src/Type/ConditionalType.php
index f154fb5368a..3819be25545 100644
--- a/src/Type/ConditionalType.php
+++ b/src/Type/ConditionalType.php
@@ -113,7 +113,13 @@ public function describe(VerbosityLevel $level): string
 
 	public function isResolvable(): bool
 	{
-		return !TypeUtils::containsTemplateType($this->subject) && !TypeUtils::containsTemplateType($this->target);
+		if (!TypeUtils::containsTemplateType($this->subject) && !TypeUtils::containsTemplateType($this->target)) {
+			return true;
+		}
+
+		$isSuperType = $this->target->isSuperTypeOf($this->subject);
+
+		return $isSuperType->yes() || $isSuperType->no();
 	}
 
 	protected function getResult(): Type
diff --git a/tests/PHPStan/Analyser/nsrt/bug-11894.php b/tests/PHPStan/Analyser/nsrt/bug-11894.php
new file mode 100644
index 00000000000..cb91f1929c1
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-11894.php
@@ -0,0 +1,70 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug11894Nsrt;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @template T
+ * @param T $a
+ * @return (T is string ? string : T)
+ */
+function conditionalReturn(mixed $a): mixed
+{
+	if (!is_string($a)) {
+		return $a;
+	}
+	return trim($a);
+}
+
+/**
+ * @template T of string|null
+ * @param T $a
+ */
+function testNarrowedToString(mixed $a): void
+{
+	if (!is_string($a)) {
+		return;
+	}
+	assertType('string', conditionalReturn($a));
+}
+
+/**
+ * @template T of int|null
+ * @param T $a
+ */
+function testNarrowedToNonMatchingType(mixed $a): void
+{
+	if (!is_int($a)) {
+		return;
+	}
+	assertType('T of int (function Bug11894Nsrt\testNarrowedToNonMatchingType(), argument)', conditionalReturn($a));
+}
+
+/**
+ * @template T of string|int
+ * @param T $a
+ */
+function testNotFullyNarrowable(mixed $a): void
+{
+	assertType('string|T of int (function Bug11894Nsrt\testNotFullyNarrowable(), argument)', conditionalReturn($a));
+}
+
+abstract class ConditionalArrayKeys
+{
+	/**
+	 * @template TKey of array-key
+	 * @template TArray of array<TKey, mixed>
+	 * @param TArray $array
+	 * @return (TArray is non-empty-array ? non-empty-list<TKey> : list<TKey>)
+	 */
+	abstract public function arrayKeys(array $array): array;
+
+	/** @param non-empty-array<int, int> $nonEmpty */
+	public function testMaybeStaysUnresolved(array $nonEmpty): void
+	{
+		assertType('non-empty-list<int>', $this->arrayKeys($nonEmpty));
+	}
+}
diff --git a/tests/PHPStan/Analyser/nsrt/bug-8048.php b/tests/PHPStan/Analyser/nsrt/bug-8048.php
new file mode 100644
index 00000000000..504605669c2
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-8048.php
@@ -0,0 +1,35 @@
+<?php declare(strict_types=1);
+
+namespace Bug8048Nsrt;
+
+use function PHPStan\Testing\assertType;
+
+interface CustomResponseInterface {}
+
+class CustomResponse implements CustomResponseInterface {}
+
+class ApiService
+{
+	/**
+	 * @template T of CustomResponseInterface
+	 *
+	 * @param class-string<T>|null $responseType
+	 *
+	 * @return ($responseType is class-string<T> ? T : null)
+	 */
+	public function request(?string $responseType = null): ?CustomResponseInterface
+	{
+		if ($responseType === null) {
+			return null;
+		}
+
+		return new CustomResponse();
+	}
+}
+
+function (): void {
+	assertType('null', (new ApiService())->request(null));
+	assertType('Bug8048Nsrt\CustomResponse', (new ApiService())->request(CustomResponse::class));
+	$x = rand(0, 1) ? CustomResponse::class : null;
+	assertType('Bug8048Nsrt\CustomResponse|null', (new ApiService())->request($x));
+};
diff --git a/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php b/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php
index 1b62fe7e8b8..f5b3ad7b2f0 100644
--- a/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php
+++ b/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php
@@ -2956,4 +2956,9 @@ public function testBug3842(): void
 		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-3842.php'], []);
 	}
 
+	public function testBug11894(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-11894.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Functions/data/bug-11894.php b/tests/PHPStan/Rules/Functions/data/bug-11894.php
new file mode 100644
index 00000000000..798919a5d6e
--- /dev/null
+++ b/tests/PHPStan/Rules/Functions/data/bug-11894.php
@@ -0,0 +1,79 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11894;
+
+/**
+ * @template T of string|null
+ * @param T $a
+ */
+function test(mixed $a): mixed
+{
+    if (!is_string($a)) {
+        return $a;
+    }
+
+	return conditionalReturn($a);
+}
+
+/**
+ * @template T
+ * @param T $a
+ * @return (T is string ? string : T)
+ */
+function conditionalReturn(mixed $a): mixed
+{
+    if (!is_string($a)) {
+        return $a;
+    }
+
+    return trim($a);
+}
+
+/**
+ * @template T of string|null
+ * @param T $a
+ */
+function testNegated(mixed $a): mixed
+{
+    if (!is_string($a)) {
+        return $a;
+    }
+
+	return conditionalReturnNegated($a);
+}
+
+/**
+ * @template T
+ * @param T $a
+ * @return (T is not string ? T : string)
+ */
+function conditionalReturnNegated(mixed $a): mixed
+{
+    if (!is_string($a)) {
+        return $a;
+    }
+
+    return trim($a);
+}
+
+/**
+ * @template T of int|null
+ * @param T $a
+ */
+function testNoRelation(mixed $a): mixed
+{
+    if (!is_int($a)) {
+        return $a;
+    }
+
+	return conditionalReturn($a);
+}
+
+/**
+ * @template T of string|int
+ * @param T $a
+ */
+function testMaybeRelation(mixed $a): mixed
+{
+	return conditionalReturn($a);
+}
diff --git a/tests/PHPStan/Rules/Methods/CallMethodsRuleTest.php b/tests/PHPStan/Rules/Methods/CallMethodsRuleTest.php
index fcf9d6d4496..141f7fbb281 100644
--- a/tests/PHPStan/Rules/Methods/CallMethodsRuleTest.php
+++ b/tests/PHPStan/Rules/Methods/CallMethodsRuleTest.php
@@ -4086,4 +4086,20 @@ public function testBug14549(): void
 		]);
 	}
 
+	public function testBug11894(): void
+	{
+		$this->checkThisOnly = false;
+		$this->checkNullables = true;
+		$this->checkUnionTypes = true;
+		$this->analyse([__DIR__ . '/data/bug-11894.php'], []);
+	}
+
+	public function testBug8048(): void
+	{
+		$this->checkThisOnly = false;
+		$this->checkNullables = true;
+		$this->checkUnionTypes = true;
+		$this->analyse([__DIR__ . '/data/bug-8048.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Methods/CallStaticMethodsRuleTest.php b/tests/PHPStan/Rules/Methods/CallStaticMethodsRuleTest.php
index 751fc0b8771..076e4770e18 100644
--- a/tests/PHPStan/Rules/Methods/CallStaticMethodsRuleTest.php
+++ b/tests/PHPStan/Rules/Methods/CallStaticMethodsRuleTest.php
@@ -1031,4 +1031,10 @@ public function testConstantParameterCheckStatic(): void
 		]);
 	}
 
+	public function testBug11894(): void
+	{
+		$this->checkThisOnly = false;
+		$this->analyse([__DIR__ . '/data/bug-11894.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Methods/data/bug-11894.php b/tests/PHPStan/Rules/Methods/data/bug-11894.php
new file mode 100644
index 00000000000..7b4daf0ada4
--- /dev/null
+++ b/tests/PHPStan/Rules/Methods/data/bug-11894.php
@@ -0,0 +1,81 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11894Methods;
+
+class Converter
+{
+	/**
+	 * @template T
+	 * @param T $a
+	 * @return (T is string ? string : T)
+	 */
+	public function conditionalReturn(mixed $a): mixed
+	{
+		if (!is_string($a)) {
+			return $a;
+		}
+		return trim($a);
+	}
+
+	/**
+	 * @template T
+	 * @param T $a
+	 * @return (T is string ? string : T)
+	 */
+	public static function conditionalReturnStatic(mixed $a): mixed
+	{
+		if (!is_string($a)) {
+			return $a;
+		}
+		return trim($a);
+	}
+}
+
+class Consumer
+{
+	/**
+	 * @template T of string|null
+	 * @param T $a
+	 */
+	public function testMethod(mixed $a): mixed
+	{
+		if (!is_string($a)) {
+			return $a;
+		}
+
+		$c = new Converter();
+		return $c->conditionalReturn($a);
+	}
+
+	/**
+	 * @template T of string|null
+	 * @param T $a
+	 */
+	public function testStaticMethod(mixed $a): mixed
+	{
+		if (!is_string($a)) {
+			return $a;
+		}
+
+		return Converter::conditionalReturnStatic($a);
+	}
+
+	/**
+	 * @template T of string|int
+	 * @param T $a
+	 */
+	public function testMaybeMethod(mixed $a): mixed
+	{
+		$c = new Converter();
+		return $c->conditionalReturn($a);
+	}
+
+	/**
+	 * @template T of string|int
+	 * @param T $a
+	 */
+	public function testMaybeStaticMethod(mixed $a): mixed
+	{
+		return Converter::conditionalReturnStatic($a);
+	}
+}
diff --git a/tests/PHPStan/Rules/Methods/data/bug-8048.php b/tests/PHPStan/Rules/Methods/data/bug-8048.php
new file mode 100644
index 00000000000..d4f7e7831ea
--- /dev/null
+++ b/tests/PHPStan/Rules/Methods/data/bug-8048.php
@@ -0,0 +1,33 @@
+<?php declare(strict_types=1);
+
+namespace Bug8048;
+
+interface CustomResponseInterface {}
+
+class CustomResponse implements CustomResponseInterface {}
+
+class ApiService
+{
+	/**
+	 * @template T of CustomResponseInterface
+	 *
+	 * @param class-string<T>|null $responseType
+	 *
+	 * @return ($responseType is class-string<T> ? T : null)
+	 */
+	public function request(?string $responseType = null): ?CustomResponseInterface
+	{
+		if ($responseType === null) {
+			return null;
+		}
+
+		return new CustomResponse();
+	}
+}
+
+function (): void {
+	(new ApiService())->request(null);
+	(new ApiService())->request(CustomResponse::class);
+	$x = rand(0, 1) ? CustomResponse::class : null;
+	(new ApiService())->request($x);
+};