diff --git a/src/Analyser/TypeSpecifier.php b/src/Analyser/TypeSpecifier.php
index 9b1e118976..084368fb4e 100644
--- a/src/Analyser/TypeSpecifier.php
+++ b/src/Analyser/TypeSpecifier.php
@@ -869,13 +869,40 @@ public function create(
 		Expr $expr,
 		Type $type,
 		TypeSpecifierContext $context,
-		bool $overwrite = false
+		bool $overwrite = false,
+		?Scope $scope = null
 	): SpecifiedTypes
 	{
 		if ($expr instanceof New_ || $expr instanceof Instanceof_) {
 			return new SpecifiedTypes();
 		}
 
+		if (
+			$expr instanceof FuncCall
+			&& $expr->name instanceof Name
+			&& $this->reflectionProvider->hasFunction($expr->name, $scope)
+		) {
+			$functionReflection = $this->reflectionProvider->getFunction($expr->name, $scope);
+			if ($functionReflection->hasSideEffects()->yes()) {
+				return new SpecifiedTypes();
+			}
+		}
+
+		if (
+			$expr instanceof MethodCall
+			&& $expr->name instanceof Node\Identifier
+			&& $scope !== null
+		) {
+			$methodName = $expr->name->toString();
+			$calledOnType = $scope->getType($expr->var);
+			if ($calledOnType->hasMethod($methodName)->yes()) {
+				$methodReflection = $calledOnType->getMethod($methodName, $scope);
+				if ($methodReflection->hasSideEffects()->yes()) {
+					return new SpecifiedTypes();
+				}
+			}
+		}
+
 		$sureTypes = [];
 		$sureNotTypes = [];
 
diff --git a/src/Rules/Comparison/ImpossibleCheckTypeHelper.php b/src/Rules/Comparison/ImpossibleCheckTypeHelper.php
index 42781da8f6..6f5cd925d3 100644
--- a/src/Rules/Comparison/ImpossibleCheckTypeHelper.php
+++ b/src/Rules/Comparison/ImpossibleCheckTypeHelper.php
@@ -179,6 +179,10 @@ public function findSpecifiedType(
 				return null;
 			}
 
+			if ($sureType[0] === $node) {
+				return null;
+			}
+
 			if ($this->treatPhpDocTypesAsCertain) {
 				$argumentType = $scope->getType($sureType[0]);
 			} else {
@@ -202,6 +206,10 @@ public function findSpecifiedType(
 				return null;
 			}
 
+			if ($sureNotType[0] === $node) {
+				return null;
+			}
+
 			if ($this->treatPhpDocTypesAsCertain) {
 				$argumentType = $scope->getType($sureNotType[0]);
 			} else {
diff --git a/tests/PHPStan/Analyser/NodeScopeResolverTest.php b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
index 8928b5ee79..a93dcb2c81 100644
--- a/tests/PHPStan/Analyser/NodeScopeResolverTest.php
+++ b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
@@ -5760,6 +5760,11 @@ public function dataBug560(): array
 		return $this->gatherAssertTypes(__DIR__ . '/data/bug-560.php');
 	}
 
+	public function dataDoNotRememberImpureFunctions(): array
+	{
+		return $this->gatherAssertTypes(__DIR__ . '/data/do-not-remember-impure-functions.php');
+	}
+
 	/**
 	 * @dataProvider dataArrayFunctions
 	 * @param string $description
@@ -11395,6 +11400,7 @@ private function gatherAssertTypes(string $file): array
 	 * @dataProvider dataBug3190
 	 * @dataProvider dataTernarySpecifiedTypes
 	 * @dataProvider dataBug560
+	 * @dataProvider dataDoNotRememberImpureFunctions
 	 * @param string $assertType
 	 * @param string $file
 	 * @param mixed ...$args
diff --git a/tests/PHPStan/Analyser/data/do-not-remember-impure-functions.php b/tests/PHPStan/Analyser/data/do-not-remember-impure-functions.php
new file mode 100644
index 0000000000..2ec0309152
--- /dev/null
+++ b/tests/PHPStan/Analyser/data/do-not-remember-impure-functions.php
@@ -0,0 +1,72 @@
+<?php
+
+namespace DoNotRememberImpureFunctions;
+
+use function PHPStan\Analyser\assertType;
+
+class Foo
+{
+
+	public function doFoo()
+	{
+		function (): void {
+			if (rand(0, 1)) {
+				assertType('int', rand(0, 1));
+			}
+		};
+
+		function (): void {
+			if (rand(0, 1) === 0) {
+				assertType('int', rand(0, 1));
+			}
+		};
+	}
+
+	public function doBar(): bool
+	{
+
+	}
+
+	/** @phpstan-pure */
+	public function doBaz(): bool
+	{
+
+	}
+
+	/** @phpstan-impure */
+	public function doLorem(): bool
+	{
+
+	}
+
+	public function doIpsum()
+	{
+		if ($this->doBar() === true) {
+			assertType('true', $this->doBar());
+		}
+
+		if ($this->doBaz() === true) {
+			assertType('true', $this->doBaz());
+		}
+
+		if ($this->doLorem() === true) {
+			assertType('bool', $this->doLorem());
+		}
+	}
+
+	public function doDolor()
+	{
+		if ($this->doBar()) {
+			assertType('true', $this->doBar());
+		}
+
+		if ($this->doBaz()) {
+			assertType('true', $this->doBaz());
+		}
+
+		if ($this->doLorem()) {
+			assertType('bool', $this->doLorem());
+		}
+	}
+
+}
diff --git a/tests/PHPStan/Analyser/data/isset.php b/tests/PHPStan/Analyser/data/isset.php
index 1497e0c56c..f78ad029b2 100644
--- a/tests/PHPStan/Analyser/data/isset.php
+++ b/tests/PHPStan/Analyser/data/isset.php
@@ -15,11 +15,11 @@ public function doFoo(array $integers, string $string, $mixedIsset, $mixedArrayK
 				'a' => 1,
 				'b' => 2,
 			];
-		} elseif (rand(0, 11) === 0) {
+		} elseif (rand(0, 10) === 0) {
 			$array = [
 				'a' => 2,
 			];
-		} elseif (rand(0, 12) === 0) {
+		} elseif (rand(0, 10) === 0) {
 			$array = [
 				'a' => 3,
 				'b' => 3,
diff --git a/tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php b/tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php
index f998a0a306..b38a6ac5ce 100644
--- a/tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php
+++ b/tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php
@@ -183,14 +183,6 @@ public function testReturnTypeRule(): void
 				'Method ReturnTypes\TrickyVoid::returnVoidOrInt() should return int|void but returns string.',
 				656,
 			],
-			[
-				'Method ReturnTypes\TernaryWithJsonEncode::toJsonOrNull() should return string|null but returns string|false|null.',
-				671,
-			],
-			[
-				'Method ReturnTypes\TernaryWithJsonEncode::toJson() should return string but returns string|false.',
-				684,
-			],
 			[
 				'Method ReturnTypes\TernaryWithJsonEncode::toJson() should return string but returns string|false.',
 				687,
@@ -235,10 +227,6 @@ public function testReturnTypeRule(): void
 				'Method ReturnTypes\WrongMagicMethods::__clone() with return type void returns int but should not return anything.',
 				757,
 			],
-			[
-				'Method ReturnTypes\ReturnSpecifiedMethodCall::doFoo() should return string but returns string|false.',
-				776,
-			],
 			[
 				'Method ReturnTypes\ArrayFillKeysIssue::getIPs2() should return array<string, array<ReturnTypes\Foo>> but returns array<string, array<int, ReturnTypes\Bar>>.',
 				815,