diff --git a/src/Symfony/Component/Yaml/Inline.php b/src/Symfony/Component/Yaml/Inline.php
index 70f4c35c44a9e..ae70ea6ec3079 100644
--- a/src/Symfony/Component/Yaml/Inline.php
+++ b/src/Symfony/Component/Yaml/Inline.php
@@ -601,9 +601,7 @@ private static function evaluateScalar(string $scalar, int $flags, array &$refer
                     case 0 === strncmp($scalar, '!php/object', 11):
                         if (self::$objectSupport) {
                             if (!isset($scalar[12])) {
-                                trigger_deprecation('symfony/yaml', '5.1', 'Using the !php/object tag without a value is deprecated.');
-
-                                return false;
+                                throw new ParseException('Missing value for tag "!php/object".', self::$parsedLineNumber + 1, $scalar, self::$parsedFilename);
                             }
 
                             return unserialize(self::parseScalar(substr($scalar, 12)));
@@ -617,9 +615,7 @@ private static function evaluateScalar(string $scalar, int $flags, array &$refer
                     case 0 === strncmp($scalar, '!php/const', 10):
                         if (self::$constantSupport) {
                             if (!isset($scalar[11])) {
-                                trigger_deprecation('symfony/yaml', '5.1', 'Using the !php/const tag without a value is deprecated.');
-
-                                return '';
+                                throw new ParseException('Missing value for tag "!php/const".', self::$parsedLineNumber + 1, $scalar, self::$parsedFilename);
                             }
 
                             $i = 0;
@@ -660,22 +656,7 @@ private static function evaluateScalar(string $scalar, int $flags, array &$refer
 
                 switch (true) {
                     case ctype_digit($scalar):
-                        if (preg_match('/^0[0-7]+$/', $scalar)) {
-                            trigger_deprecation('symfony/yaml', '5.1', 'Support for parsing numbers prefixed with 0 as octal numbers. They will be parsed as strings as of 6.0.');
-
-                            return octdec($scalar);
-                        }
-
-                        $cast = (int) $scalar;
-
-                        return ($scalar === (string) $cast) ? $cast : $scalar;
                     case '-' === $scalar[0] && ctype_digit(substr($scalar, 1)):
-                        if (preg_match('/^-0[0-7]+$/', $scalar)) {
-                            trigger_deprecation('symfony/yaml', '5.1', 'Support for parsing numbers prefixed with 0 as octal numbers. They will be parsed as strings as of 6.0.');
-
-                            return -octdec(substr($scalar, 1));
-                        }
-
                         $cast = (int) $scalar;
 
                         return ($scalar === (string) $cast) ? $cast : $scalar;
diff --git a/src/Symfony/Component/Yaml/Tests/InlineTest.php b/src/Symfony/Component/Yaml/Tests/InlineTest.php
index e6e61981900e2..5e7451ba7228a 100644
--- a/src/Symfony/Component/Yaml/Tests/InlineTest.php
+++ b/src/Symfony/Component/Yaml/Tests/InlineTest.php
@@ -757,92 +757,73 @@ public function getTestsForOctalNumbers()
     }
 
     /**
-     * @group legacy
      * @dataProvider getTestsForOctalNumbersYaml11Notation
      */
-    public function testParseOctalNumbersYaml11Notation(int $expected, string $yaml)
+    public function testParseOctalNumbersYaml11Notation(string $expected, string $yaml)
     {
-        $this->expectDeprecation('Since symfony/yaml 5.1: Support for parsing numbers prefixed with 0 as octal numbers. They will be parsed as strings as of 6.0.');
-
         self::assertSame($expected, Inline::parse($yaml));
     }
 
     public function getTestsForOctalNumbersYaml11Notation()
     {
         return [
-            'positive octal number' => [28, '034'],
-            'positive octal number with separator' => [1243, '0_2_3_3_3'],
-            'negative octal number' => [-28, '-034'],
+            'positive octal number' => ['034', '034'],
+            'positive octal number with separator' => ['02333', '0_2_3_3_3'],
+            'negative octal number' => ['-034', '-034'],
+            'invalid positive octal number' => ['0123456789', '0123456789'],
+            'invalid negative octal number' => ['-0123456789', '-0123456789'],
         ];
     }
 
     /**
      * @dataProvider phpObjectTagWithEmptyValueProvider
-     *
-     * @group legacy
      */
-    public function testPhpObjectWithEmptyValue($expected, $value)
+    public function testPhpObjectWithEmptyValue(string $value)
     {
-        $this->expectDeprecation('Since symfony/yaml 5.1: Using the !php/object tag without a value is deprecated.');
+        $this->expectException(ParseException::class);
+        $this->expectExceptionMessage('Missing value for tag "!php/object" at line 1 (near "!php/object").');
 
-        $this->assertSame($expected, Inline::parse($value, Yaml::PARSE_OBJECT));
+        Inline::parse($value, Yaml::PARSE_OBJECT);
     }
 
     public function phpObjectTagWithEmptyValueProvider()
     {
         return [
-            [false, '!php/object'],
-            [false, '!php/object '],
-            [false, '!php/object  '],
-            [[false], '[!php/object]'],
-            [[false], '[!php/object ]'],
-            [[false, 'foo'], '[!php/object  , foo]'],
+            ['!php/object'],
+            ['!php/object '],
+            ['!php/object  '],
+            ['[!php/object]'],
+            ['[!php/object ]'],
+            ['[!php/object  , foo]'],
         ];
     }
 
     /**
      * @dataProvider phpConstTagWithEmptyValueProvider
-     *
-     * @group legacy
      */
-    public function testPhpConstTagWithEmptyValue($expected, $value)
+    public function testPhpConstTagWithEmptyValue(string $value)
     {
-        $this->expectDeprecation('Since symfony/yaml 5.1: Using the !php/const tag without a value is deprecated.');
+        $this->expectException(ParseException::class);
+        $this->expectExceptionMessage('Missing value for tag "!php/const" at line 1 (near "!php/const").');
 
-        $this->assertSame($expected, Inline::parse($value, Yaml::PARSE_CONSTANT));
+        Inline::parse($value, Yaml::PARSE_CONSTANT);
     }
 
     public function phpConstTagWithEmptyValueProvider()
     {
         return [
-            ['', '!php/const'],
-            ['', '!php/const '],
-            ['', '!php/const  '],
-            [[''], '[!php/const]'],
-            [[''], '[!php/const ]'],
-            [['', 'foo'], '[!php/const  , foo]'],
-            [['' => 'foo'], '{!php/const: foo}'],
-            [['' => 'foo'], '{!php/const : foo}'],
-            [['' => 'foo', 'bar' => 'ccc'], '{!php/const  : foo, bar: ccc}'],
+            ['!php/const'],
+            ['!php/const '],
+            ['!php/const  '],
+            ['[!php/const]'],
+            ['[!php/const ]'],
+            ['[!php/const  , foo]'],
+            ['{!php/const: foo}'],
+            ['{!php/const : foo}'],
+            ['{!php/const  : foo, bar: ccc}'],
         ];
     }
 
-    /**
-     * @group legacy
-     */
-    public function testParsePositiveOctalNumberContainingInvalidDigits()
-    {
-        self::assertSame('0123456789', Inline::parse('0123456789'));
-    }
-
-    /**
-     * @group legacy
-     */
-    public function testParseNegativeOctalNumberContainingInvalidDigits()
-    {
-        self::assertSame('-0123456789', Inline::parse('-0123456789'));
-    }
-
     public function testParseCommentNotPrefixedBySpaces()
     {
         self::assertSame('foo', Inline::parse('"foo"#comment'));