diff --git a/packages/eslint-plugin/src/rules/no-magic-numbers.ts b/packages/eslint-plugin/src/rules/no-magic-numbers.ts
index 1f45a489d357..ac079f62d43c 100644
--- a/packages/eslint-plugin/src/rules/no-magic-numbers.ts
+++ b/packages/eslint-plugin/src/rules/no-magic-numbers.ts
@@ -1,6 +1,6 @@
 import {
-  TSESTree,
   AST_NODE_TYPES,
+  TSESTree,
 } from '@typescript-eslint/experimental-utils';
 import baseRule from 'eslint/lib/rules/no-magic-numbers';
 import * as util from '../util';
@@ -8,9 +8,23 @@ import * as util from '../util';
 type Options = util.InferOptionsTypeFromRule<typeof baseRule>;
 type MessageIds = util.InferMessageIdsTypeFromRule<typeof baseRule>;
 
-const baseRuleSchema = Array.isArray(baseRule.meta.schema)
-  ? baseRule.meta.schema[0]
-  : baseRule.meta.schema;
+// Extend base schema with additional property to ignore TS numeric literal types
+const schema = util.deepMerge(
+  { ...baseRule.meta.schema },
+  {
+    properties: {
+      ignoreNumericLiteralTypes: {
+        type: 'boolean',
+      },
+      ignoreEnums: {
+        type: 'boolean',
+      },
+      ignoreReadonlyClassProperties: {
+        type: 'boolean',
+      },
+    },
+  },
+);
 
 export default util.createRule<Options, MessageIds>({
   name: 'no-magic-numbers',
@@ -22,24 +36,7 @@ export default util.createRule<Options, MessageIds>({
       recommended: false,
       extendsBaseRule: true,
     },
-    // Extend base schema with additional property to ignore TS numeric literal types
-    schema: [
-      {
-        ...baseRuleSchema,
-        properties: {
-          ...baseRuleSchema.properties,
-          ignoreNumericLiteralTypes: {
-            type: 'boolean',
-          },
-          ignoreEnums: {
-            type: 'boolean',
-          },
-          ignoreReadonlyClassProperties: {
-            type: 'boolean',
-          },
-        },
-      },
-    ],
+    schema: [schema],
     messages: baseRule.meta.messages ?? {
       useConst: "Number constants declarations must use 'const'.",
       noMagic: 'No magic number: {{raw}}.',
diff --git a/packages/experimental-utils/src/ts-eslint/Rule.ts b/packages/experimental-utils/src/ts-eslint/Rule.ts
index 24b8fd4fa114..bdabc3fe883d 100644
--- a/packages/experimental-utils/src/ts-eslint/Rule.ts
+++ b/packages/experimental-utils/src/ts-eslint/Rule.ts
@@ -73,15 +73,15 @@ interface RuleMetaData<TMessageIds extends string> {
   /**
    * The name of the rule this rule was replaced by, if it was deprecated.
    */
-  replacedBy?: string[];
+  replacedBy?: readonly string[];
   /**
    * The options schema. Supply an empty array if there are no options.
    */
-  schema: JSONSchema4 | JSONSchema4[];
+  schema: JSONSchema4 | readonly JSONSchema4[];
 }
 
 interface RuleFix {
-  range: AST.Range;
+  range: Readonly<AST.Range>;
   text: string;
 }
 
@@ -91,25 +91,25 @@ interface RuleFixer {
     text: string,
   ): RuleFix;
 
-  insertTextAfterRange(range: AST.Range, text: string): RuleFix;
+  insertTextAfterRange(range: Readonly<AST.Range>, text: string): RuleFix;
 
   insertTextBefore(
     nodeOrToken: TSESTree.Node | TSESTree.Token,
     text: string,
   ): RuleFix;
 
-  insertTextBeforeRange(range: AST.Range, text: string): RuleFix;
+  insertTextBeforeRange(range: Readonly<AST.Range>, text: string): RuleFix;
 
   remove(nodeOrToken: TSESTree.Node | TSESTree.Token): RuleFix;
 
-  removeRange(range: AST.Range): RuleFix;
+  removeRange(range: Readonly<AST.Range>): RuleFix;
 
   replaceText(
     nodeOrToken: TSESTree.Node | TSESTree.Token,
     text: string,
   ): RuleFix;
 
-  replaceTextRange(range: AST.Range, text: string): RuleFix;
+  replaceTextRange(range: Readonly<AST.Range>, text: string): RuleFix;
 }
 
 type ReportFixFunction = (
@@ -209,13 +209,13 @@ interface RuleContext<
    * the root of the AST and continuing through the direct parent of the current node.
    * This array does not include the currently-traversed node itself.
    */
-  getAncestors(): TSESTree.Node[];
+  getAncestors(): readonly TSESTree.Node[];
 
   /**
    * Returns a list of variables declared by the given node.
    * This information can be used to track references to variables.
    */
-  getDeclaredVariables(node: TSESTree.Node): Scope.Variable[];
+  getDeclaredVariables(node: TSESTree.Node): readonly Scope.Variable[];
 
   /**
    * Returns the current working directory passed to Linter.