diff --git a/src/Symfony/Component/String/AbstractUnicodeString.php b/src/Symfony/Component/String/AbstractUnicodeString.php
index bc0c7f8763..ce1c8094ab 100644
--- a/src/Symfony/Component/String/AbstractUnicodeString.php
+++ b/src/Symfony/Component/String/AbstractUnicodeString.php
@@ -348,14 +348,11 @@ abstract class AbstractUnicodeString extends AbstractString
     {
         $str = clone $this;
 
-        if ($allWords) {
-            $str->string = preg_replace_callback('/\b./u', static function ($m) {
-                return mb_convert_case($m[0], MB_CASE_TITLE, 'UTF-8');
-            }, $str->string);
-        } else {
-            $firstChar = mb_substr($str->string, 0, 1, 'UTF-8');
-            $str->string = mb_convert_case($firstChar, MB_CASE_TITLE, 'UTF-8').substr($str->string, \strlen($firstChar));
-        }
+        $limit = $allWords ? -1 : 1;
+
+        $str->string = preg_replace_callback('/\b./u', static function (array $m): string {
+            return mb_convert_case($m[0], MB_CASE_TITLE, 'UTF-8');
+        }, $str->string, $limit);
 
         return $str;
     }
diff --git a/src/Symfony/Component/String/Tests/AbstractUnicodeTestCase.php b/src/Symfony/Component/String/Tests/AbstractUnicodeTestCase.php
index 836a296854..173abd026a 100644
--- a/src/Symfony/Component/String/Tests/AbstractUnicodeTestCase.php
+++ b/src/Symfony/Component/String/Tests/AbstractUnicodeTestCase.php
@@ -292,6 +292,19 @@ abstract class AbstractUnicodeTestCase extends AbstractAsciiTestCase
                 ['DEJa', 'dEJa', false],
                 ['ΣσΣ', 'σσΣ', false],
                 ['Deja Σσς DEJa ΣσΣ', 'deja σσς dEJa σσΣ', true],
+
+                // Spanish
+                ['Última prueba', 'última prueba', false],
+                ['ÚLTIMA pRUEBA', 'úLTIMA pRUEBA', false],
+
+                ['¡Hola spain!', '¡hola spain!', false],
+                ['¡HOLA sPAIN!', '¡hOLA sPAIN!', false],
+
+                ['¡Hola Spain!', '¡hola spain!', true],
+                ['¡HOLA SPAIN!', '¡hOLA sPAIN!', true],
+
+                ['Última Prueba', 'última prueba', true],
+                ['ÚLTIMA PRUEBA', 'úLTIMA pRUEBA', true],
             ]
         );
     }