diff --git a/src/Analyser/TypeSpecifier.php b/src/Analyser/TypeSpecifier.php
index a71997abed..1079fc1b53 100644
--- a/src/Analyser/TypeSpecifier.php
+++ b/src/Analyser/TypeSpecifier.php
@@ -30,6 +30,7 @@
 use PHPStan\Type\Accessory\HasOffsetType;
 use PHPStan\Type\Accessory\HasPropertyType;
 use PHPStan\Type\Accessory\NonEmptyArrayType;
+use PHPStan\Type\ArrayType;
 use PHPStan\Type\BooleanType;
 use PHPStan\Type\ConditionalTypeForParameter;
 use PHPStan\Type\Constant\ConstantArrayType;
@@ -52,6 +53,7 @@
 use PHPStan\Type\NullType;
 use PHPStan\Type\ObjectType;
 use PHPStan\Type\ObjectWithoutClassType;
+use PHPStan\Type\ResourceType;
 use PHPStan\Type\StaticMethodTypeSpecifyingExtension;
 use PHPStan\Type\StaticType;
 use PHPStan\Type\StaticTypeFactory;
@@ -286,6 +288,44 @@ public function specifyTypesInCondition(
 						);
 					}
 				}
+
+				if (
+					$exprNode instanceof FuncCall
+					&& $exprNode->name instanceof Name
+					&& strtolower($exprNode->name->toString()) === 'gettype'
+					&& isset($exprNode->getArgs()[0])
+					&& $constantType instanceof ConstantStringType
+				) {
+					$type = null;
+					if ($constantType->getValue() === 'string') {
+						$type = new StringType();
+					}
+					if ($constantType->getValue() === 'array') {
+						$type = new ArrayType(new MixedType(), new MixedType());
+					}
+					if ($constantType->getValue() === 'boolean') {
+						$type = new BooleanType();
+					}
+					if ($constantType->getValue() === 'resource' || $constantType->getValue() === 'resource (closed)') {
+						$type = new ResourceType();
+					}
+					if ($constantType->getValue() === 'integer') {
+						$type = new IntegerType();
+					}
+					if ($constantType->getValue() === 'double') {
+						$type = new FloatType();
+					}
+					if ($constantType->getValue() === 'NULL') {
+						$type = new NullType();
+					}
+					if ($constantType->getValue() === 'object') {
+						$type = new ObjectWithoutClassType();
+					}
+
+					if ($type !== null) {
+						return $this->create($exprNode->getArgs()[0]->value, $type, $context, false, $scope, $rootExpr);
+					}
+				}
 			}
 
 			$rightType = $scope->getType($expr->right);
@@ -407,6 +447,17 @@ public function specifyTypesInCondition(
 						$rootExpr,
 					);
 				}
+
+				if (
+					$exprNode instanceof FuncCall
+					&& $exprNode->name instanceof Name
+					&& strtolower($exprNode->name->toString()) === 'gettype'
+					&& isset($exprNode->getArgs()[0])
+					&& $constantType instanceof ConstantStringType
+				) {
+					return $this->specifyTypesInCondition($scope, new Expr\BinaryOp\Identical($expr->left, $expr->right), $context, $rootExpr);
+				}
+
 			}
 
 			$leftType = $scope->getType($expr->left);
diff --git a/tests/PHPStan/Analyser/NodeScopeResolverTest.php b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
index 152420e240..654cd8b617 100644
--- a/tests/PHPStan/Analyser/NodeScopeResolverTest.php
+++ b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
@@ -969,6 +969,7 @@ public function dataFileAsserts(): iterable
 		yield from $this->gatherAssertTypes(__DIR__ . '/../Rules/Variables/data/bug-7417.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/../Rules/Arrays/data/bug-7469.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/../Rules/Variables/data/bug-3391.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6901.php');
 	}
 
 	/**
diff --git a/tests/PHPStan/Analyser/data/bug-6901.php b/tests/PHPStan/Analyser/data/bug-6901.php
new file mode 100644
index 0000000000..8f818b9035
--- /dev/null
+++ b/tests/PHPStan/Analyser/data/bug-6901.php
@@ -0,0 +1,97 @@
+<?php
+
+namespace Bug6901;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param integer|string|array<string>|bool $y
+ * @return integer
+ */
+function foo($y)
+{
+	switch (gettype($y)) {
+		case "integer":
+			assertType('int', $y);
+			break;
+		case "string":
+			assertType('string', $y);
+			break;
+		case "boolean":
+			assertType('bool', $y);
+			break;
+		case "array":
+			assertType('array<string>', $y);
+			break;
+		default:
+			assertType('*NEVER*', $y);
+	}
+	assertType('array<string>|bool|int|string', $y);
+	return 0;
+}
+
+/**
+ * @param object|float|null|resource $y
+ * @return integer
+ */
+function bar($y)
+{
+	switch (gettype($y)) {
+		case "object":
+			assertType('object', $y);
+			break;
+		case "double":
+			assertType('float', $y);
+			break;
+		case "NULL":
+			assertType('null', $y);
+			break;
+		case "resource":
+			assertType('resource', $y);
+			break;
+		default:
+			assertType('*NEVER*', $y);
+	}
+	assertType('float|object|resource|null', $y);
+	return 0;
+}
+
+/**
+ * @param int|string|bool $x
+ * @param int|string|bool $y
+ */
+function foobarIdentical($x, $y)
+{
+	if (gettype($x) === 'integer') {
+		assertType('int', $x);
+		return;
+	}
+	assertType('bool|string', $x);
+
+	if ('boolean' === gettype($x)) {
+		assertType('bool', $x);
+		return;
+	}
+
+	if (gettype($y) === 'string' || gettype($y) === 'integer') {
+		assertType('int|string', $y);
+	}
+}
+
+/**
+ * @param int|string|bool $x
+ */
+function foobarEqual($x)
+{
+	if (gettype($x) == 'integer') {
+		assertType('int', $x);
+		return;
+	}
+
+	if ('boolean' == gettype($x)) {
+		assertType('bool', $x);
+		return;
+	}
+	
+	assertType('string', $x);
+}