diff --git a/packages/eslint-plugin/src/rules/unified-signatures.ts b/packages/eslint-plugin/src/rules/unified-signatures.ts
index b387450801f..3b5f2294762 100644
--- a/packages/eslint-plugin/src/rules/unified-signatures.ts
+++ b/packages/eslint-plugin/src/rules/unified-signatures.ts
@@ -213,7 +213,8 @@ export default util.createRule<Options, MessageIds>({
         b.typeParameters !== undefined ? b.typeParameters.params : undefined;
 
       if (ignoreDifferentlyNamedParameters) {
-        for (let i = 0; i < a.params.length; i += 1) {
+        const commonParamsLength = Math.min(a.params.length, b.params.length);
+        for (let i = 0; i < commonParamsLength; i += 1) {
           if (
             a.params[i].type === b.params[i].type &&
             getStaticParameterName(a.params[i]) !==
diff --git a/packages/eslint-plugin/tests/rules/unified-signatures.test.ts b/packages/eslint-plugin/tests/rules/unified-signatures.test.ts
index 73f773dc42d..ce62f6c571c 100644
--- a/packages/eslint-plugin/tests/rules/unified-signatures.test.ts
+++ b/packages/eslint-plugin/tests/rules/unified-signatures.test.ts
@@ -177,6 +177,28 @@ function f(v: number, u?: string): void {}
     },
     {
       code: `
+function f(v: boolean): number;
+function f(): string;
+      `,
+      options: [{ ignoreDifferentlyNamedParameters: true }],
+    },
+    {
+      code: `
+function f(v: boolean, u: boolean): number;
+function f(v: boolean): string;
+      `,
+      options: [{ ignoreDifferentlyNamedParameters: true }],
+    },
+    {
+      code: `
+function f(v: number, u?: string): void {}
+function f(v: number): void;
+function f(): string;
+      `,
+      options: [{ ignoreDifferentlyNamedParameters: true }],
+    },
+    {
+      code: `
 function f(a: boolean, ...c: number[]): void;
 function f(a: boolean, ...d: string[]): void;
 function f(a: boolean, ...c: (number | string)[]): void {}