diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
index 1662d1fa9a..ee382d508b 100644
--- a/phpstan-baseline.neon
+++ b/phpstan-baseline.neon
@@ -1040,11 +1040,6 @@ parameters:
 			count: 3
 			path: src/Type/Generic/TemplateIntersectionType.php
 
-		-
-			message: "#^Instanceof between PHPStan\\\\Type\\\\Type and PHPStan\\\\Type\\\\IntersectionType will always evaluate to false\\.$#"
-			count: 2
-			path: src/Type/Generic/TemplateIntersectionType.php
-
 		-
 			message: "#^Doing instanceof PHPStan\\\\Type\\\\IntersectionType is error\\-prone and deprecated\\.$#"
 			count: 3
@@ -1145,11 +1140,6 @@ parameters:
 			count: 3
 			path: src/Type/Generic/TemplateUnionType.php
 
-		-
-			message: "#^Instanceof between PHPStan\\\\Type\\\\Type and PHPStan\\\\Type\\\\UnionType will always evaluate to false\\.$#"
-			count: 2
-			path: src/Type/Generic/TemplateUnionType.php
-
 		-
 			message: "#^Doing instanceof PHPStan\\\\Type\\\\ConstantScalarType is error\\-prone and deprecated\\. Use Type\\:\\:isConstantScalarValue\\(\\) or Type\\:\\:getConstantScalarTypes\\(\\) or Type\\:\\:getConstantScalarValues\\(\\) instead\\.$#"
 			count: 1
diff --git a/src/Analyser/TypeSpecifier.php b/src/Analyser/TypeSpecifier.php
index 088236bac5..f7d01f2da6 100644
--- a/src/Analyser/TypeSpecifier.php
+++ b/src/Analyser/TypeSpecifier.php
@@ -156,14 +156,17 @@ public function specifyTypesInCondition(
 			}
 
 			$classType = $scope->getType($expr->class);
-			$type = TypeTraverser::map($classType, static function (Type $type, callable $traverse): Type {
+			$uncertainty = false;
+			$type = TypeTraverser::map($classType, static function (Type $type, callable $traverse) use (&$uncertainty): Type {
 				if ($type instanceof UnionType || $type instanceof IntersectionType) {
 					return $traverse($type);
 				}
 				if ($type->getObjectClassNames() !== []) {
+					$uncertainty = true;
 					return $type;
 				}
 				if ($type instanceof GenericClassStringType) {
+					$uncertainty = true;
 					return $type->getGenericType();
 				}
 				if ($type instanceof ConstantStringType) {
@@ -179,7 +182,7 @@ public function specifyTypesInCondition(
 						new ObjectWithoutClassType(),
 					);
 					return $this->create($exprNode, $type, $context, false, $scope, $rootExpr);
-				} elseif ($context->false()) {
+				} elseif ($context->false() && !$uncertainty) {
 					$exprType = $scope->getType($expr->expr);
 					if (!$type->isSuperTypeOf($exprType)->yes()) {
 						return $this->create($exprNode, $type, $context, false, $scope, $rootExpr);
diff --git a/tests/PHPStan/Analyser/nsrt/bug-12107.php b/tests/PHPStan/Analyser/nsrt/bug-12107.php
new file mode 100644
index 0000000000..1a2c839c05
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-12107.php
@@ -0,0 +1,43 @@
+<?php declare(strict_types = 1);
+
+namespace Bug12107;
+
+use LogicException;
+use Throwable;
+
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+	public function sayHello(Throwable $e1, LogicException $e2): void
+	{
+		if ($e1 instanceof $e2) {
+			return;
+		}
+
+		assertType('Throwable', $e1);
+		assertType('bool', $e1 instanceof $e2); // could be false
+	}
+
+	/** @param class-string<LogicException> $e2 */
+	public function sayHello2(Throwable $e1, string $e2): void
+	{
+		if ($e1 instanceof $e2) {
+			return;
+		}
+
+
+		assertType('Throwable', $e1);
+		assertType('bool', $e1 instanceof $e2); // could be false
+	}
+
+	public function sayHello3(Throwable $e1): void
+	{
+		if ($e1 instanceof LogicException) {
+			return;
+		}
+
+		assertType('Throwable~LogicException', $e1);
+		assertType('false', $e1 instanceof LogicException);
+	}
+}
diff --git a/tests/PHPStan/Analyser/nsrt/instanceof-class-string.php b/tests/PHPStan/Analyser/nsrt/instanceof-class-string.php
index dc2bcaa2f3..22c58c4b20 100644
--- a/tests/PHPStan/Analyser/nsrt/instanceof-class-string.php
+++ b/tests/PHPStan/Analyser/nsrt/instanceof-class-string.php
@@ -32,7 +32,7 @@ public function doBar(Foo $foo, Bar $bar): void
 		if ($foo instanceof $class) {
 			assertType(self::class, $foo);
 		} else {
-			assertType('InstanceOfClassString\Foo~InstanceOfClassString\Bar', $foo);
+			assertType('InstanceOfClassString\Foo', $foo);
 		}
 	}
 
diff --git a/tests/PHPStan/Analyser/nsrt/instanceof.php b/tests/PHPStan/Analyser/nsrt/instanceof.php
index 098b74cb47..9ad5cceea7 100644
--- a/tests/PHPStan/Analyser/nsrt/instanceof.php
+++ b/tests/PHPStan/Analyser/nsrt/instanceof.php
@@ -80,9 +80,9 @@ public function testExprInstanceof($subject, string $classString, $union, $inter
 			assertType('true', $subject instanceof Foo);
 			assertType('bool', $subject instanceof $classString);
 		} else {
-			assertType('mixed~InstanceOfNamespace\Foo', $subject);
-			assertType('false', $subject instanceof Foo);
-			assertType('false', $subject instanceof $classString);
+			assertType('mixed', $subject);
+			assertType('bool', $subject instanceof Foo);
+			assertType('bool', $subject instanceof $classString); // could be false
 		}
 
 		$constantString = 'InstanceOfNamespace\BarParent';
@@ -132,7 +132,7 @@ public function testExprInstanceof($subject, string $classString, $union, $inter
 			assertType('ObjectT of InstanceOfNamespace\BarInterface (method InstanceOfNamespace\Foo::testExprInstanceof(), argument)', $subject);
 			assertType('bool', $subject instanceof $objectT);
 		} else {
-			assertType('mixed~ObjectT of InstanceOfNamespace\BarInterface (method InstanceOfNamespace\Foo::testExprInstanceof(), argument)', $subject);
+			assertType('mixed', $subject);
 			assertType('bool', $subject instanceof $objectT); // can be false
 		}
 
@@ -140,7 +140,7 @@ public function testExprInstanceof($subject, string $classString, $union, $inter
 			assertType('ObjectT of InstanceOfNamespace\BarInterface (method InstanceOfNamespace\Foo::testExprInstanceof(), argument)', $subject);
 			assertType('bool', $subject instanceof $objectTString);
 		} else {
-			assertType('mixed~ObjectT of InstanceOfNamespace\BarInterface (method InstanceOfNamespace\Foo::testExprInstanceof(), argument)', $subject);
+			assertType('mixed', $subject);
 			assertType('bool', $subject instanceof $objectTString); // can be false
 		}
 
@@ -148,7 +148,7 @@ public function testExprInstanceof($subject, string $classString, $union, $inter
 			assertType('MixedT (method InstanceOfNamespace\Foo::testExprInstanceof(), argument)&object', $subject);
 			assertType('bool', $subject instanceof $mixedTString);
 		} else {
-			assertType('mixed~MixedT (method InstanceOfNamespace\Foo::testExprInstanceof(), argument)', $subject);
+			assertType('mixed', $subject);
 			assertType('bool', $subject instanceof $mixedTString); // can be false
 		}
 
@@ -180,8 +180,8 @@ public function testExprInstanceof($subject, string $classString, $union, $inter
 			assertType('InstanceOfNamespace\Foo', $object);
 			assertType('bool', $object instanceof $classString);
 		} else {
-			assertType('object~InstanceOfNamespace\Foo', $object);
-			assertType('false', $object instanceof $classString);
+			assertType('object', $object);
+			assertType('bool', $object instanceof $classString); // could be false
 		}
 
 		if ($instance instanceof $string) {
diff --git a/tests/PHPStan/Rules/Classes/ImpossibleInstanceOfRuleTest.php b/tests/PHPStan/Rules/Classes/ImpossibleInstanceOfRuleTest.php
index fde28cab1a..5382491c02 100644
--- a/tests/PHPStan/Rules/Classes/ImpossibleInstanceOfRuleTest.php
+++ b/tests/PHPStan/Rules/Classes/ImpossibleInstanceOfRuleTest.php
@@ -167,11 +167,6 @@ public function testInstanceof(): void
 					388,
 					$tipText,
 				],
-				[
-					'Instanceof between T of Exception and Error will always evaluate to false.',
-					404,
-					$tipText,
-				],
 				[
 					'Instanceof between class-string<DateTimeInterface> and DateTimeInterface will always evaluate to false.',
 					418,
@@ -270,11 +265,6 @@ public function testInstanceofWithoutAlwaysTrue(): void
 					'Instanceof between mixed and ImpossibleInstanceOf\InvalidTypeTest|int results in an error.',
 					362,
 				],*/
-				[
-					'Instanceof between T of Exception and Error will always evaluate to false.',
-					404,
-					$tipText,
-				],
 				[
 					'Instanceof between class-string<DateTimeInterface> and DateTimeInterface will always evaluate to false.',
 					418,