diff --git a/src/Symfony/Component/OptionsResolver/OptionsResolver.php b/src/Symfony/Component/OptionsResolver/OptionsResolver.php
index 8935ef6fdb..8401bc08a1 100644
--- a/src/Symfony/Component/OptionsResolver/OptionsResolver.php
+++ b/src/Symfony/Component/OptionsResolver/OptionsResolver.php
@@ -163,7 +163,7 @@ class OptionsResolver implements Options
      *
      * @throws AccessException If called from a lazy option or normalizer
      */
-    public function setDefault($option, $value)
+    public function setDefault(string $option, $value)
     {
         // Setting is not possible once resolving starts, because then lazy
         // options could manipulate the state of the object, leading to
@@ -257,7 +257,7 @@ class OptionsResolver implements Options
      *
      * @return bool Whether a default value is set
      */
-    public function hasDefault($option)
+    public function hasDefault(string $option)
     {
         return \array_key_exists($option, $this->defaults);
     }
@@ -294,7 +294,7 @@ class OptionsResolver implements Options
      *
      * @return bool Whether the option is required
      */
-    public function isRequired($option)
+    public function isRequired(string $option)
     {
         return isset($this->required[$option]);
     }
@@ -322,7 +322,7 @@ class OptionsResolver implements Options
      *
      * @return bool Whether the option is missing
      */
-    public function isMissing($option)
+    public function isMissing(string $option)
     {
         return isset($this->required[$option]) && !\array_key_exists($option, $this->defaults);
     }
@@ -375,7 +375,7 @@ class OptionsResolver implements Options
      *
      * @return bool Whether the option is defined
      */
-    public function isDefined($option)
+    public function isDefined(string $option)
     {
         return isset($this->defined[$option]);
     }
@@ -474,7 +474,7 @@ class OptionsResolver implements Options
      * @throws UndefinedOptionsException If the option is undefined
      * @throws AccessException           If called from a lazy option or normalizer
      */
-    public function setNormalizer($option, \Closure $normalizer)
+    public function setNormalizer(string $option, \Closure $normalizer)
     {
         if ($this->locked) {
             throw new AccessException('Normalizers cannot be set from a lazy option or normalizer.');
@@ -562,7 +562,7 @@ class OptionsResolver implements Options
      * @throws UndefinedOptionsException If the option is undefined
      * @throws AccessException           If called from a lazy option or normalizer
      */
-    public function setAllowedValues($option, $allowedValues)
+    public function setAllowedValues(string $option, $allowedValues)
     {
         if ($this->locked) {
             throw new AccessException('Allowed values cannot be set from a lazy option or normalizer.');
@@ -603,7 +603,7 @@ class OptionsResolver implements Options
      * @throws UndefinedOptionsException If the option is undefined
      * @throws AccessException           If called from a lazy option or normalizer
      */
-    public function addAllowedValues($option, $allowedValues)
+    public function addAllowedValues(string $option, $allowedValues)
     {
         if ($this->locked) {
             throw new AccessException('Allowed values cannot be added from a lazy option or normalizer.');
@@ -644,7 +644,7 @@ class OptionsResolver implements Options
      * @throws UndefinedOptionsException If the option is undefined
      * @throws AccessException           If called from a lazy option or normalizer
      */
-    public function setAllowedTypes($option, $allowedTypes)
+    public function setAllowedTypes(string $option, $allowedTypes)
     {
         if ($this->locked) {
             throw new AccessException('Allowed types cannot be set from a lazy option or normalizer.');
@@ -679,7 +679,7 @@ class OptionsResolver implements Options
      * @throws UndefinedOptionsException If the option is undefined
      * @throws AccessException           If called from a lazy option or normalizer
      */
-    public function addAllowedTypes($option, $allowedTypes)
+    public function addAllowedTypes(string $option, $allowedTypes)
     {
         if ($this->locked) {
             throw new AccessException('Allowed types cannot be added from a lazy option or normalizer.');