diff --git a/src/ExpressionParser.php b/src/ExpressionParser.php
index 73bdbc73b..38cbdd8a2 100644
--- a/src/ExpressionParser.php
+++ b/src/ExpressionParser.php
@@ -27,6 +27,8 @@ use Twig\Node\Expression\Unary\NegUnary;
 use Twig\Node\Expression\Unary\NotUnary;
 use Twig\Node\Expression\Unary\PosUnary;
 use Twig\Node\Node;
+use Twig\Node\Expression\AbstractExpression;
+use Twig\Node\Expression\TestExpression;
 
 /**
  * Parses expressions.
@@ -88,7 +90,7 @@ class ExpressionParser
         return $expr;
     }
 
-    private function getPrimary()
+    private function getPrimary(): AbstractExpression
     {
         $token = $this->parser->getCurrentToken();
 
@@ -110,7 +112,7 @@ class ExpressionParser
         return $this->parsePrimaryExpression();
     }
 
-    private function parseConditionalExpression($expr)
+    private function parseConditionalExpression($expr): AbstractExpression
     {
         while ($this->parser->getStream()->nextIf(/* Token::PUNCTUATION_TYPE */ 9, '?')) {
             if (!$this->parser->getStream()->nextIf(/* Token::PUNCTUATION_TYPE */ 9, ':')) {
@@ -131,12 +133,12 @@ class ExpressionParser
         return $expr;
     }
 
-    private function isUnary(Token $token)
+    private function isUnary(Token $token): bool
     {
         return $token->test(/* Token::OPERATOR_TYPE */ 8) && isset($this->unaryOperators[$token->getValue()]);
     }
 
-    private function isBinary(Token $token)
+    private function isBinary(Token $token): bool
     {
         return $token->test(/* Token::OPERATOR_TYPE */ 8) && isset($this->binaryOperators[$token->getValue()]);
     }
@@ -598,12 +600,12 @@ class ExpressionParser
         return new Node($targets);
     }
 
-    private function parseNotTestExpression(Node $node)
+    private function parseNotTestExpression(Node $node): NotUnary
     {
         return new NotUnary($this->parseTestExpression($node), $this->parser->getCurrentToken()->getLine());
     }
 
-    private function parseTestExpression(Node $node)
+    private function parseTestExpression(Node $node): TestExpression
     {
         $stream = $this->parser->getStream();
         list($name, $test) = $this->getTest($node->getTemplateLine());
@@ -617,7 +619,7 @@ class ExpressionParser
         return new $class($node, $name, $arguments, $this->parser->getCurrentToken()->getLine());
     }
 
-    private function getTest($line)
+    private function getTest(int $line): array
     {
         $stream = $this->parser->getStream();
         $name = $stream->expect(/* Token::NAME_TYPE */ 5)->getValue();
@@ -643,7 +645,7 @@ class ExpressionParser
         throw $e;
     }
 
-    private function getTestNodeClass($test)
+    private function getTestNodeClass(TwigTest $test): string
     {
         if ($test->isDeprecated()) {
             $stream = $this->parser->getStream();
@@ -664,7 +666,7 @@ class ExpressionParser
         return $test->getNodeClass();
     }
 
-    private function getFunctionNodeClass($name, $line)
+    private function getFunctionNodeClass(string $name, int $line): string
     {
         if (false === $function = $this->env->getFunction($name)) {
             $e = new SyntaxError(sprintf('Unknown "%s" function.', $name), $line, $this->parser->getStream()->getSourceContext());
@@ -690,7 +692,7 @@ class ExpressionParser
         return $function->getNodeClass();
     }
 
-    private function getFilterNodeClass($name, $line)
+    private function getFilterNodeClass(string $name, int $line): string
     {
         if (false === $filter = $this->env->getFilter($name)) {
             $e = new SyntaxError(sprintf('Unknown "%s" filter.', $name), $line, $this->parser->getStream()->getSourceContext());
@@ -717,7 +719,7 @@ class ExpressionParser
     }
 
     // checks that the node only contains "constant" elements
-    private function checkConstantExpression(Node $node)
+    private function checkConstantExpression(Node $node): bool
     {
         if (!($node instanceof ConstantExpression || $node instanceof ArrayExpression
             || $node instanceof NegUnary || $node instanceof PosUnary
diff --git a/src/Node/Expression/BlockReferenceExpression.php b/src/Node/Expression/BlockReferenceExpression.php
index d370229a9..839186dee 100644
--- a/src/Node/Expression/BlockReferenceExpression.php
+++ b/src/Node/Expression/BlockReferenceExpression.php
@@ -49,7 +49,7 @@ class BlockReferenceExpression extends AbstractExpression
         }
     }
 
-    private function compileTemplateCall(Compiler $compiler, $method)
+    private function compileTemplateCall(Compiler $compiler, string $method): Compiler
     {
         if (!$this->hasNode('template')) {
             $compiler->write('$this');
@@ -66,12 +66,11 @@ class BlockReferenceExpression extends AbstractExpression
         }
 
         $compiler->raw(sprintf('->%s', $method));
-        $this->compileBlockArguments($compiler);
 
-        return $compiler;
+        return $this->compileBlockArguments($compiler);
     }
 
-    private function compileBlockArguments(Compiler $compiler)
+    private function compileBlockArguments(Compiler $compiler): Compiler
     {
         $compiler
             ->raw('(')
diff --git a/src/Node/Expression/CallExpression.php b/src/Node/Expression/CallExpression.php
index 59be15b21..69c505855 100644
--- a/src/Node/Expression/CallExpression.php
+++ b/src/Node/Expression/CallExpression.php
@@ -230,7 +230,7 @@ abstract class CallExpression extends AbstractExpression
         return strtolower(preg_replace(['/([A-Z]+)([A-Z][a-z])/', '/([a-z\d])([A-Z])/'], ['\\1_\\2', '\\1_\\2'], $name));
     }
 
-    private function getCallableParameters($callable, $isVariadic)
+    private function getCallableParameters($callable, bool $isVariadic): array
     {
         list($r) = $this->reflectCallable($callable);
         if (null === $r) {
diff --git a/src/NodeTraverser.php b/src/NodeTraverser.php
index e4146fc0b..42cced4b4 100644
--- a/src/NodeTraverser.php
+++ b/src/NodeTraverser.php
@@ -59,7 +59,7 @@ final class NodeTraverser
         return $node;
     }
 
-    private function traverseForVisitor(NodeVisitorInterface $visitor, Node $node)
+    private function traverseForVisitor(NodeVisitorInterface $visitor, Node $node): Node
     {
         $node = $visitor->enterNode($node, $this->env);
 
diff --git a/src/NodeVisitor/EscaperNodeVisitor.php b/src/NodeVisitor/EscaperNodeVisitor.php
index df1704d12..940ef8b30 100644
--- a/src/NodeVisitor/EscaperNodeVisitor.php
+++ b/src/NodeVisitor/EscaperNodeVisitor.php
@@ -147,7 +147,7 @@ final class EscaperNodeVisitor extends AbstractNodeVisitor
         return $this->defaultStrategy ? $this->defaultStrategy : false;
     }
 
-    private function getEscaperFilter($type, Node $node)
+    private function getEscaperFilter(string $type, Node $node): FilterExpression
     {
         $line = $node->getTemplateLine();
         $name = new ConstantExpression('escape', $line);
diff --git a/src/NodeVisitor/OptimizerNodeVisitor.php b/src/NodeVisitor/OptimizerNodeVisitor.php
index a829aa285..4bf7f7470 100644
--- a/src/NodeVisitor/OptimizerNodeVisitor.php
+++ b/src/NodeVisitor/OptimizerNodeVisitor.php
@@ -90,10 +90,8 @@ final class OptimizerNodeVisitor extends AbstractNodeVisitor
      * It replaces:
      *
      *   * "echo $this->render(Parent)Block()" with "$this->display(Parent)Block()"
-     *
-     * @return Node
      */
-    private function optimizePrintNode(Node $node, Environment $env)
+    private function optimizePrintNode(Node $node, Environment $env): Node
     {
         if (!$node instanceof PrintNode) {
             return $node;
@@ -114,10 +112,8 @@ final class OptimizerNodeVisitor extends AbstractNodeVisitor
 
     /**
      * Removes "raw" filters.
-     *
-     * @return Node
      */
-    private function optimizeRawFilter(Node $node, Environment $env)
+    private function optimizeRawFilter(Node $node, Environment $env): Node
     {
         if ($node instanceof FilterExpression && 'raw' == $node->getNode('filter')->getAttribute('value')) {
             return $node->getNode('node');
diff --git a/src/NodeVisitor/SafeAnalysisNodeVisitor.php b/src/NodeVisitor/SafeAnalysisNodeVisitor.php
index d0b0539de..02a2af436 100644
--- a/src/NodeVisitor/SafeAnalysisNodeVisitor.php
+++ b/src/NodeVisitor/SafeAnalysisNodeVisitor.php
@@ -134,7 +134,7 @@ final class SafeAnalysisNodeVisitor extends AbstractNodeVisitor
         return $node;
     }
 
-    private function intersectSafe(array $a = null, array $b = null)
+    private function intersectSafe(array $a = null, array $b = null): array
     {
         if (null === $a || null === $b) {
             return [];
diff --git a/src/NodeVisitor/SandboxNodeVisitor.php b/src/NodeVisitor/SandboxNodeVisitor.php
index aa229564e..9fb432d68 100644
--- a/src/NodeVisitor/SandboxNodeVisitor.php
+++ b/src/NodeVisitor/SandboxNodeVisitor.php
@@ -110,7 +110,7 @@ final class SandboxNodeVisitor extends AbstractNodeVisitor
         return $node;
     }
 
-    private function wrapNode(Node $node, $name)
+    private function wrapNode(Node $node, string $name)
     {
         $expr = $node->getNode($name);
         if ($expr instanceof NameExpression || $expr instanceof GetAttrExpression) {
@@ -118,7 +118,7 @@ final class SandboxNodeVisitor extends AbstractNodeVisitor
         }
     }
 
-    private function wrapArrayNode(Node $node, $name)
+    private function wrapArrayNode(Node $node, string $name)
     {
         $args = $node->getNode($name);
         foreach ($args as $name => $_) {
diff --git a/src/Parser.php b/src/Parser.php
index 89193d516..e93df8d0b 100644
--- a/src/Parser.php
+++ b/src/Parser.php
@@ -335,7 +335,7 @@ class Parser
         return $this->stream->getCurrent();
     }
 
-    private function filterBodyNodes(Node $node, $nested = false)
+    private function filterBodyNodes(Node $node, bool $nested = false)
     {
         // check that the body does not contain non-empty output nodes
         if (
diff --git a/src/Profiler/Dumper/BaseDumper.php b/src/Profiler/Dumper/BaseDumper.php
index d965dc754..1631987bb 100644
--- a/src/Profiler/Dumper/BaseDumper.php
+++ b/src/Profiler/Dumper/BaseDumper.php
@@ -31,7 +31,7 @@ abstract class BaseDumper
 
     abstract protected function formatTime(Profile $profile, $percent);
 
-    private function dumpProfile(Profile $profile, $prefix = '', $sibling = false)
+    private function dumpProfile(Profile $profile, $prefix = '', $sibling = false): string
     {
         if ($profile->isRoot()) {
             $this->root = $profile->getDuration();
diff --git a/src/Profiler/Dumper/BlackfireDumper.php b/src/Profiler/Dumper/BlackfireDumper.php
index 05d937baf..f33342905 100644
--- a/src/Profiler/Dumper/BlackfireDumper.php
+++ b/src/Profiler/Dumper/BlackfireDumper.php
@@ -40,7 +40,7 @@ EOF;
         return $str;
     }
 
-    private function dumpChildren($parent, Profile $profile, &$data)
+    private function dumpChildren(string $parent, Profile $profile, &$data)
     {
         foreach ($profile as $p) {
             if ($p->isTemplate()) {
@@ -53,7 +53,7 @@ EOF;
         }
     }
 
-    private function dumpProfile($edge, Profile $profile, &$data)
+    private function dumpProfile(string $edge, Profile $profile, &$data)
     {
         if (isset($data[$edge])) {
             ++$data[$edge]['ct'];
diff --git a/src/Profiler/NodeVisitor/ProfilerNodeVisitor.php b/src/Profiler/NodeVisitor/ProfilerNodeVisitor.php
index a5416004f..fcfcdd20f 100644
--- a/src/Profiler/NodeVisitor/ProfilerNodeVisitor.php
+++ b/src/Profiler/NodeVisitor/ProfilerNodeVisitor.php
@@ -64,7 +64,7 @@ final class ProfilerNodeVisitor extends AbstractNodeVisitor
         return $node;
     }
 
-    private function getVarName()
+    private function getVarName(): string
     {
         return sprintf('__internal_%s', hash('sha256', $this->extensionName));
     }