diff --git a/rules/sort-classes.ts b/rules/sort-classes.ts
index e08bd0798..3be6d45b5 100644
--- a/rules/sort-classes.ts
+++ b/rules/sort-classes.ts
@@ -680,11 +680,6 @@ export default createEslintRule<SortClassesOptions, MESSAGE_ID>({
         pairwise(nodes, (left, right) => {
           let leftNum = getGroupNumber(options.groups, left)
           let rightNum = getGroupNumber(options.groups, right)
-          // Ignore nodes belonging to `unknown` group when that group is not referenced in the
-          // `groups` option.
-          let isLeftOrRightIgnored =
-            leftNum === options.groups.length ||
-            rightNum === options.groups.length
 
           let indexOfLeft = sortedNodes.indexOf(left)
           let indexOfRight = sortedNodes.indexOf(right)
@@ -692,7 +687,7 @@ export default createEslintRule<SortClassesOptions, MESSAGE_ID>({
             getFirstUnorderedNodeDependentOn(right, nodes)
           if (
             firstUnorderedNodeDependentOnRight ||
-            (!isLeftOrRightIgnored && indexOfLeft > indexOfRight)
+            indexOfLeft > indexOfRight
           ) {
             let messageId: MESSAGE_ID
             if (firstUnorderedNodeDependentOnRight) {
diff --git a/test/sort-classes.test.ts b/test/sort-classes.test.ts
index d3fd2a2a3..cf60f5c02 100644
--- a/test/sort-classes.test.ts
+++ b/test/sort-classes.test.ts
@@ -3923,6 +3923,77 @@ describe(ruleName, () => {
                 rightGroup: 'private-method',
               },
             },
+            {
+              messageId: 'unexpectedClassesGroupOrder',
+              data: {
+                left: 'z',
+                leftGroup: 'private-method',
+                right: 'method3',
+                rightGroup: 'unknown',
+              },
+            },
+            {
+              messageId: 'unexpectedClassesGroupOrder',
+              data: {
+                left: 'method3',
+                leftGroup: 'unknown',
+                right: 'y',
+                rightGroup: 'private-method',
+              },
+            },
+            {
+              messageId: 'unexpectedClassesGroupOrder',
+              data: {
+                left: 'method1',
+                leftGroup: 'unknown',
+                right: 'x',
+                rightGroup: 'private-method',
+              },
+            },
+          ],
+        },
+        {
+          code: dedent`
+              class Class {
+                b
+                someMethod() {
+                }
+                a
+              }
+            `,
+          output: dedent`
+              class Class {
+                a
+                someMethod() {
+                }
+                b
+              }
+            `,
+          options: [
+            {
+              ...options,
+              groups: ['property'],
+            },
+          ],
+          errors: [
+            {
+              messageId: 'unexpectedClassesGroupOrder',
+              data: {
+                left: 'b',
+                leftGroup: 'property',
+                right: 'someMethod',
+                rightGroup: 'unknown',
+              },
+            },
+            {
+              messageId: 'unexpectedClassesGroupOrder',
+              data: {
+                left: 'someMethod',
+                leftGroup: 'unknown',
+                right: 'a',
+                rightGroup: 'property',
+              },
+            },
           ],
         },
       ],
@@ -5135,6 +5206,77 @@ describe(ruleName, () => {
                 rightGroup: 'private-method',
               },
             },
+            {
+              messageId: 'unexpectedClassesGroupOrder',
+              data: {
+                left: 'z',
+                leftGroup: 'private-method',
+                right: 'method3',
+                rightGroup: 'unknown',
+              },
+            },
+            {
+              messageId: 'unexpectedClassesGroupOrder',
+              data: {
+                left: 'method3',
+                leftGroup: 'unknown',
+                right: 'y',
+                rightGroup: 'private-method',
+              },
+            },
+            {
+              messageId: 'unexpectedClassesGroupOrder',
+              data: {
+                left: 'method1',
+                leftGroup: 'unknown',
+                right: 'x',
+                rightGroup: 'private-method',
+              },
+            },
+          ],
+        },
+        {
+          code: dedent`
+              class Class {
+                b
+                someMethod() {
+                }
+                a
+              }
+            `,
+          output: dedent`
+              class Class {
+                a
+                someMethod() {
+                }
+                b
+              }
+            `,
+          options: [
+            {
+              ...options,
+              groups: ['property'],
+            },
+          ],
+          errors: [
+            {
+              messageId: 'unexpectedClassesGroupOrder',
+              data: {
+                left: 'b',
+                leftGroup: 'property',
+                right: 'someMethod',
+                rightGroup: 'unknown',
+              },
+            },
+            {
+              messageId: 'unexpectedClassesGroupOrder',
+              data: {
+                left: 'someMethod',
+                leftGroup: 'unknown',
+                right: 'a',
+                rightGroup: 'property',
+              },
+            },
           ],
         },
       ],
@@ -5970,6 +6112,24 @@ describe(ruleName, () => {
                 rightGroup: 'private-method',
               },
             },
+            {
+              messageId: 'unexpectedClassesGroupOrder',
+              data: {
+                left: 'method3',
+                leftGroup: 'unknown',
+                right: 'y',
+                rightGroup: 'private-method',
+              },
+            },
+            {
+              messageId: 'unexpectedClassesGroupOrder',
+              data: {
+                left: 'method1',
+                leftGroup: 'unknown',
+                right: 'x',
+                rightGroup: 'private-method',
+              },
+            },
           ],
         },
       ],