diff --git a/src/Ruleset.php b/src/Ruleset.php
index 9a9f959163..b6279bf9f3 100644
--- a/src/Ruleset.php
+++ b/src/Ruleset.php
@@ -1409,6 +1409,24 @@ public function registerSniffs($files, $restrictions, $exclusions)
                 continue;
             }
 
+            if ($reflection->implementsInterface('PHP_CodeSniffer\Sniffs\Sniff') === false) {
+                // Skip classes which don't implement the register() or process() methods.
+                if (method_exists($className, 'register') === false
+                    || method_exists($className, 'process') === false
+                ) {
+                    $errorMsg = 'Sniff class %s is missing required method %s().';
+                    if (method_exists($className, 'register') === false) {
+                        $this->msgCache->add(sprintf($errorMsg, $className, 'register'), MessageCollector::ERROR);
+                    }
+
+                    if (method_exists($className, 'process') === false) {
+                        $this->msgCache->add(sprintf($errorMsg, $className, 'process'), MessageCollector::ERROR);
+                    }
+
+                    continue;
+                }
+            }//end if
+
             $listeners[$className] = $className;
 
             if (PHP_CODESNIFFER_VERBOSITY > 2) {
diff --git a/tests/Core/Ruleset/Fixtures/TestStandard/Sniffs/InvalidSniffError/NoImplementsNoProcessSniff.php b/tests/Core/Ruleset/Fixtures/TestStandard/Sniffs/InvalidSniffError/NoImplementsNoProcessSniff.php
new file mode 100644
index 0000000000..d6aa4ee6a8
--- /dev/null
+++ b/tests/Core/Ruleset/Fixtures/TestStandard/Sniffs/InvalidSniffError/NoImplementsNoProcessSniff.php
@@ -0,0 +1,17 @@
+<?php
+/**
+ * Test fixture.
+ *
+ * @see \PHP_CodeSniffer\Tests\Core\Ruleset\RegisterSniffsRejectsInvalidSniffTest
+ */
+
+namespace Fixtures\TestStandard\Sniffs\InvalidSniffError;
+
+final class NoImplementsNoProcessSniff
+{
+
+    public function register()
+    {
+        return [T_OPEN_TAG];
+    }
+}
diff --git a/tests/Core/Ruleset/Fixtures/TestStandard/Sniffs/InvalidSniffError/NoImplementsNoRegisterOrProcessSniff.php b/tests/Core/Ruleset/Fixtures/TestStandard/Sniffs/InvalidSniffError/NoImplementsNoRegisterOrProcessSniff.php
new file mode 100644
index 0000000000..b13c70eb96
--- /dev/null
+++ b/tests/Core/Ruleset/Fixtures/TestStandard/Sniffs/InvalidSniffError/NoImplementsNoRegisterOrProcessSniff.php
@@ -0,0 +1,12 @@
+<?php
+/**
+ * Test fixture.
+ *
+ * @see \PHP_CodeSniffer\Tests\Core\Ruleset\RegisterSniffsRejectsInvalidSniffTest
+ */
+
+namespace Fixtures\TestStandard\Sniffs\InvalidSniffError;
+
+final class NoImplementsNoRegisterOrProcessSniff
+{
+}
diff --git a/tests/Core/Ruleset/Fixtures/TestStandard/Sniffs/InvalidSniffError/NoImplementsNoRegisterSniff.php b/tests/Core/Ruleset/Fixtures/TestStandard/Sniffs/InvalidSniffError/NoImplementsNoRegisterSniff.php
new file mode 100644
index 0000000000..9f55064272
--- /dev/null
+++ b/tests/Core/Ruleset/Fixtures/TestStandard/Sniffs/InvalidSniffError/NoImplementsNoRegisterSniff.php
@@ -0,0 +1,19 @@
+<?php
+/**
+ * Test fixture.
+ *
+ * @see \PHP_CodeSniffer\Tests\Core\Ruleset\RegisterSniffsRejectsInvalidSniffTest
+ */
+
+namespace Fixtures\TestStandard\Sniffs\InvalidSniffError;
+
+use PHP_CodeSniffer\Files\File;
+
+final class NoImplementsNoRegisterSniff
+{
+
+    public function process(File $phpcsFile, $stackPtr)
+    {
+        // Do something.
+    }
+}
diff --git a/tests/Core/Ruleset/ProcessRulesetAutoExpandSniffsDirectoryTest.xml b/tests/Core/Ruleset/ProcessRulesetAutoExpandSniffsDirectoryTest.xml
index 579b9485d2..3b8b4c9b41 100644
--- a/tests/Core/Ruleset/ProcessRulesetAutoExpandSniffsDirectoryTest.xml
+++ b/tests/Core/Ruleset/ProcessRulesetAutoExpandSniffsDirectoryTest.xml
@@ -5,6 +5,7 @@
 
     <rule ref="TestStandard">
         <exclude name="TestStandard.InvalidSniffs"/>
+        <exclude name="TestStandard.InvalidSniffError"/>
     </rule>
 
 </ruleset>
diff --git a/tests/Core/Ruleset/RegisterSniffsRejectsInvalidSniffNoImplementsNoProcessTest.xml b/tests/Core/Ruleset/RegisterSniffsRejectsInvalidSniffNoImplementsNoProcessTest.xml
new file mode 100644
index 0000000000..6b70d32d85
--- /dev/null
+++ b/tests/Core/Ruleset/RegisterSniffsRejectsInvalidSniffNoImplementsNoProcessTest.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0"?>
+<ruleset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" name="RegisterSniffsRejectsInvalidSniffTest" xsi:noNamespaceSchemaLocation="https://raw.githubusercontent.com/PHPCSStandards/PHP_CodeSniffer/master/phpcs.xsd">
+
+    <rule ref="./tests/Core/Ruleset/Fixtures/TestStandard/Sniffs/InvalidSniffError/NoImplementsNoProcessSniff.php"/>
+
+    <!-- Prevent a "no sniff were registered" error. -->
+    <rule ref="Generic.PHP.BacktickOperator"/>
+</ruleset>
diff --git a/tests/Core/Ruleset/RegisterSniffsRejectsInvalidSniffNoImplementsNoRegisterOrProcessTest.xml b/tests/Core/Ruleset/RegisterSniffsRejectsInvalidSniffNoImplementsNoRegisterOrProcessTest.xml
new file mode 100644
index 0000000000..06e2028375
--- /dev/null
+++ b/tests/Core/Ruleset/RegisterSniffsRejectsInvalidSniffNoImplementsNoRegisterOrProcessTest.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0"?>
+<ruleset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" name="RegisterSniffsRejectsInvalidSniffTest" xsi:noNamespaceSchemaLocation="https://raw.githubusercontent.com/PHPCSStandards/PHP_CodeSniffer/master/phpcs.xsd">
+
+    <rule ref="./tests/Core/Ruleset/Fixtures/TestStandard/Sniffs/InvalidSniffError/NoImplementsNoRegisterOrProcessSniff.php"/>
+
+    <!-- Prevent a "no sniff were registered" error. -->
+    <rule ref="Generic.PHP.BacktickOperator"/>
+</ruleset>
diff --git a/tests/Core/Ruleset/RegisterSniffsRejectsInvalidSniffNoImplementsNoRegisterTest.xml b/tests/Core/Ruleset/RegisterSniffsRejectsInvalidSniffNoImplementsNoRegisterTest.xml
new file mode 100644
index 0000000000..9e0913f9cc
--- /dev/null
+++ b/tests/Core/Ruleset/RegisterSniffsRejectsInvalidSniffNoImplementsNoRegisterTest.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0"?>
+<ruleset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" name="RegisterSniffsRejectsInvalidSniffTest" xsi:noNamespaceSchemaLocation="https://raw.githubusercontent.com/PHPCSStandards/PHP_CodeSniffer/master/phpcs.xsd">
+
+    <rule ref="./tests/Core/Ruleset/Fixtures/TestStandard/Sniffs/InvalidSniffError/NoImplementsNoRegisterSniff.php"/>
+
+    <!-- Prevent a "no sniff were registered" error. -->
+    <rule ref="Generic.PHP.BacktickOperator"/>
+</ruleset>
diff --git a/tests/Core/Ruleset/RegisterSniffsRejectsInvalidSniffTest.php b/tests/Core/Ruleset/RegisterSniffsRejectsInvalidSniffTest.php
new file mode 100644
index 0000000000..1efe5cdba0
--- /dev/null
+++ b/tests/Core/Ruleset/RegisterSniffsRejectsInvalidSniffTest.php
@@ -0,0 +1,80 @@
+<?php
+/**
+ * Tests that invalid sniffs will be rejected with an informative error message.
+ *
+ * @author    Juliette Reinders Folmer <phpcs_nospam@adviesenzo.nl>
+ * @copyright 2025 PHPCSStandards and contributors
+ * @license   https://github.com/PHPCSStandards/PHP_CodeSniffer/blob/master/licence.txt BSD Licence
+ */
+
+namespace PHP_CodeSniffer\Tests\Core\Ruleset;
+
+use PHP_CodeSniffer\Ruleset;
+use PHP_CodeSniffer\Tests\ConfigDouble;
+use PHP_CodeSniffer\Tests\Core\Ruleset\AbstractRulesetTestCase;
+
+/**
+ * Tests that invalid sniffs will be rejected with an informative error message.
+ *
+ * @covers \PHP_CodeSniffer\Ruleset::registerSniffs
+ */
+final class RegisterSniffsRejectsInvalidSniffTest extends AbstractRulesetTestCase
+{
+
+
+    /**
+     * Verify that an error is thrown if an invalid sniff class is loaded.
+     *
+     * @param string $standard   The standard to use for the test.
+     * @param string $methodName The name of the missing method.
+     *
+     * @dataProvider dataExceptionIsThrownOnMissingInterfaceMethod
+     *
+     * @return void
+     */
+    public function testExceptionIsThrownOnMissingInterfaceMethod($standard, $methodName)
+    {
+        // Set up the ruleset.
+        $standard = __DIR__.'/'.$standard;
+        $config   = new ConfigDouble(["--standard=$standard"]);
+
+        $regex = "`(^|\R)ERROR: Sniff class \S+Sniff is missing required method $methodName\(\)\.\R`";
+        $this->expectRuntimeExceptionRegex($regex);
+
+        new Ruleset($config);
+
+    }//end testExceptionIsThrownOnMissingInterfaceMethod()
+
+
+    /**
+     * Data provider.
+     *
+     * @see testExceptionIsThrownOnMissingInterfaceMethod()
+     *
+     * @return array<string, array<string, string>>
+     */
+    public static function dataExceptionIsThrownOnMissingInterfaceMethod()
+    {
+        return [
+            'Missing register() method'                => [
+                'standard'   => 'RegisterSniffsRejectsInvalidSniffNoImplementsNoRegisterTest.xml',
+                'methodName' => 'register',
+            ],
+            'Missing process() method'                 => [
+                'standard'   => 'RegisterSniffsRejectsInvalidSniffNoImplementsNoProcessTest.xml',
+                'methodName' => 'process',
+            ],
+            'Missing both, checking register() method' => [
+                'standard'   => 'RegisterSniffsRejectsInvalidSniffNoImplementsNoRegisterOrProcessTest.xml',
+                'methodName' => 'register',
+            ],
+            'Missing both, checking process() method'  => [
+                'standard'   => 'RegisterSniffsRejectsInvalidSniffNoImplementsNoRegisterOrProcessTest.xml',
+                'methodName' => 'process',
+            ],
+        ];
+
+    }//end dataExceptionIsThrownOnMissingInterfaceMethod()
+
+
+}//end class
diff --git a/tests/Core/Ruleset/ShowSniffDeprecationsTest.xml b/tests/Core/Ruleset/ShowSniffDeprecationsTest.xml
index 802bd3c0a9..ab632b1959 100644
--- a/tests/Core/Ruleset/ShowSniffDeprecationsTest.xml
+++ b/tests/Core/Ruleset/ShowSniffDeprecationsTest.xml
@@ -6,6 +6,7 @@
     <rule ref="TestStandard">
         <exclude name="TestStandard.DeprecatedInvalid"/>
         <exclude name="TestStandard.InvalidSniffs"/>
+        <exclude name="TestStandard.InvalidSniffError"/>
     </rule>
 
 </ruleset>