diff --git a/packages/eslint-plugin/src/rules/interface-name-prefix.ts b/packages/eslint-plugin/src/rules/interface-name-prefix.ts
index 175cbf41c3b..b9c3b91a052 100644
--- a/packages/eslint-plugin/src/rules/interface-name-prefix.ts
+++ b/packages/eslint-plugin/src/rules/interface-name-prefix.ts
@@ -1,7 +1,7 @@
 import * as util from '../util';
 
 type Options = ['never' | 'always'];
-type MessageIds = 'noPrefix';
+type MessageIds = 'noPrefix' | 'alwaysPrefix';
 
 export default util.createRule<Options, MessageIds>({
   name: 'interface-name-prefix',
@@ -15,6 +15,7 @@ export default util.createRule<Options, MessageIds>({
     },
     messages: {
       noPrefix: 'Interface name must not be prefixed with "I".',
+      alwaysPrefix: 'Interface name must be prefixed with "I".',
     },
     schema: [
       {
@@ -51,7 +52,7 @@ export default util.createRule<Options, MessageIds>({
           if (!isPrefixedWithI(node.id.name)) {
             context.report({
               node: node.id,
-              messageId: 'noPrefix',
+              messageId: 'alwaysPrefix',
             });
           }
         }
diff --git a/packages/eslint-plugin/tests/rules/interface-name-prefix.test.ts b/packages/eslint-plugin/tests/rules/interface-name-prefix.test.ts
index d954d160fa9..09cf548c7ac 100644
--- a/packages/eslint-plugin/tests/rules/interface-name-prefix.test.ts
+++ b/packages/eslint-plugin/tests/rules/interface-name-prefix.test.ts
@@ -77,7 +77,7 @@ interface Animal {
       options: ['always'],
       errors: [
         {
-          messageId: 'noPrefix',
+          messageId: 'alwaysPrefix',
           line: 2,
           column: 11,
         },
@@ -92,7 +92,7 @@ interface Iguana {
       options: ['always'],
       errors: [
         {
-          messageId: 'noPrefix',
+          messageId: 'alwaysPrefix',
           line: 2,
           column: 11,
         },