diff --git a/packages/mermaid/src/Diagram.ts b/packages/mermaid/src/Diagram.ts
index 0aa741994..d6c226cde 100644
--- a/packages/mermaid/src/Diagram.ts
+++ b/packages/mermaid/src/Diagram.ts
@@ -2,15 +2,17 @@ import * as configApi from './config';
 import { log } from './logger';
 import { getDiagram, registerDiagram } from './diagram-api/diagramAPI';
 import { detectType, getDiagramLoader } from './diagram-api/detectType';
-import { isDetailedError } from './utils';
+import { isDetailedError, type DetailedError } from './utils';
+
+export type ParseErrorFunction = (err: string | DetailedError, hash?: any) => void;
+
 export class Diagram {
   type = 'graph';
   parser;
   renderer;
   db;
   private detectTypeFailed = false;
-  // eslint-disable-next-line @typescript-eslint/ban-types
-  constructor(public txt: string, parseError?: Function) {
+  constructor(public txt: string, parseError?: ParseErrorFunction) {
     const cnf = configApi.getConfig();
     this.txt = txt;
     try {
@@ -37,8 +39,7 @@ export class Diagram {
     this.parse(this.txt, parseError);
   }
 
-  // eslint-disable-next-line @typescript-eslint/ban-types
-  parse(text: string, parseError?: Function): boolean {
+  parse(text: string, parseError?: ParseErrorFunction): boolean {
     if (this.detectTypeFailed) {
       return false;
     }
@@ -53,23 +54,24 @@ export class Diagram {
     return false;
   }
 
-  // eslint-disable-next-line @typescript-eslint/ban-types
-  handleError(error: unknown, parseError?: Function) {
+  handleError(error: unknown, parseError?: ParseErrorFunction) {
     // Is this the correct way to access mermiad's parseError()
     // method ? (or global.mermaid.parseError()) ?
-    if (parseError) {
-      if (isDetailedError(error)) {
-        // handle case where error string and hash were
-        // wrapped in object like`const error = { str, hash };`
-        parseError(error.str, error.hash);
-      } else {
-        // assume it is just error string and pass it on
-        parseError(error);
-      }
-    } else {
+
+    if (parseError === undefined) {
       // No mermaid.parseError() handler defined, so re-throw it
       throw error;
     }
+
+    if (isDetailedError(error)) {
+      // Handle case where error string and hash were
+      // wrapped in object like`const error = { str, hash };`
+      parseError(error.str, error.hash);
+      return;
+    }
+
+    // Otherwise, assume it is just an error string and pass it on
+    parseError(error as string);
   }
 
   getParser() {
@@ -81,8 +83,10 @@ export class Diagram {
   }
 }
 
-// eslint-disable-next-line @typescript-eslint/ban-types
-export const getDiagramFromText = async (txt: string, parseError?: Function): Promise<Diagram> => {
+export const getDiagramFromText = async (
+  txt: string,
+  parseError?: ParseErrorFunction
+): Promise<Diagram> => {
   const type = detectType(txt, configApi.getConfig());
   try {
     // Trying to find the diagram
diff --git a/packages/mermaid/src/__mocks__/mermaidAPI.ts b/packages/mermaid/src/__mocks__/mermaidAPI.ts
index 08c5b7eea..3102095b9 100644
--- a/packages/mermaid/src/__mocks__/mermaidAPI.ts
+++ b/packages/mermaid/src/__mocks__/mermaidAPI.ts
@@ -6,7 +6,7 @@
 import * as configApi from '../config';
 import { vi } from 'vitest';
 import { addDiagrams } from '../diagram-api/diagram-orchestration';
-import Diagram from '../Diagram';
+import Diagram, { type ParseErrorFunction } from '../Diagram';
 
 // Normally, we could just do the following to get the original `parse()`
 // implementation, however, requireActual returns a promise and it's not documented how to use withing mock file.
@@ -15,8 +15,7 @@ import Diagram from '../Diagram';
  * @param text
  * @param parseError
  */
-// eslint-disable-next-line @typescript-eslint/ban-types
-function parse(text: string, parseError?: Function): boolean {
+function parse(text: string, parseError?: ParseErrorFunction): boolean {
   addDiagrams();
   const diagram = new Diagram(text, parseError);
   return diagram.parse(text, parseError);
diff --git a/packages/mermaid/src/mermaid.ts b/packages/mermaid/src/mermaid.ts
index ae6c62547..09842c426 100644
--- a/packages/mermaid/src/mermaid.ts
+++ b/packages/mermaid/src/mermaid.ts
@@ -8,6 +8,7 @@ import utils from './utils';
 import { mermaidAPI } from './mermaidAPI';
 import { addDetector } from './diagram-api/detectType';
 import { isDetailedError } from './utils';
+import type { ParseErrorFunction } from './Diagram';
 
 /**
  * ## init
@@ -62,7 +63,7 @@ const init = async function (
       log.warn(e.str);
     }
     if (mermaid.parseError) {
-      mermaid.parseError(e);
+      mermaid.parseError(e as string);
     }
   }
 };
@@ -212,8 +213,7 @@ const parse = (txt: string) => {
 const mermaid: {
   startOnLoad: boolean;
   diagrams: any;
-  // eslint-disable-next-line @typescript-eslint/ban-types
-  parseError?: Function;
+  parseError?: ParseErrorFunction;
   mermaidAPI: typeof mermaidAPI;
   parse: typeof parse;
   render: typeof mermaidAPI.render;
diff --git a/packages/mermaid/src/mermaidAPI.ts b/packages/mermaid/src/mermaidAPI.ts
index 7c967e5fd..7fe5064de 100644
--- a/packages/mermaid/src/mermaidAPI.ts
+++ b/packages/mermaid/src/mermaidAPI.ts
@@ -22,7 +22,7 @@ import classDb from './diagrams/class/classDb';
 import flowDb from './diagrams/flowchart/flowDb';
 import flowRenderer from './diagrams/flowchart/flowRenderer';
 import ganttDb from './diagrams/gantt/ganttDb';
-import Diagram, { getDiagramFromText } from './Diagram';
+import Diagram, { getDiagramFromText, type ParseErrorFunction } from './Diagram';
 import errorRenderer from './diagrams/error/errorRenderer';
 import { attachFunctions } from './interactionDb';
 import { log, setLogLevel } from './logger';
@@ -37,8 +37,7 @@ import { evaluate } from './diagrams/common/common';
  * @param text
  * @param parseError
  */
-// eslint-disable-next-line @typescript-eslint/ban-types
-function parse(text: string, parseError?: Function): boolean {
+function parse(text: string, parseError?: ParseErrorFunction): boolean {
   addDiagrams();
   const diagram = new Diagram(text, parseError);
   return diagram.parse(text, parseError);