diff --git a/CHANGELOG.md b/CHANGELOG.md
index 188b038f..e2f0c3f3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,6 +19,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 ### Fixed
 * [#766](https://github.com/shlinkio/shlink-web-client/issues/766) Fixed visits query being lost when switching between sub-sections.
+* [#765](https://github.com/shlinkio/shlink-web-client/issues/765) Added missing `"Content-Type": "application/json"` to requests with payload, making older Shlink versions fail.
 
 
 ## [3.8.1] - 2022-12-06
diff --git a/src/common/services/HttpClient.ts b/src/common/services/HttpClient.ts
index af8aedf3..9a07cfea 100644
--- a/src/common/services/HttpClient.ts
+++ b/src/common/services/HttpClient.ts
@@ -1,10 +1,27 @@
 import { Fetch } from '../../utils/types';
 
+const applicationJsonHeader = { 'Content-Type': 'application/json' };
+const withJsonContentType = (options?: RequestInit): RequestInit | undefined => {
+  if (!options?.body) {
+    return options;
+  }
+
+  return options ? {
+    ...options,
+    headers: {
+      ...(options.headers ?? {}),
+      ...applicationJsonHeader,
+    },
+  } : {
+    headers: applicationJsonHeader,
+  };
+};
+
 export class HttpClient {
   constructor(private readonly fetch: Fetch) {}
 
   public readonly fetchJson = <T>(url: string, options?: RequestInit): Promise<T> =>
-    this.fetch(url, options).then(async (resp) => {
+    this.fetch(url, withJsonContentType(options)).then(async (resp) => {
       const json = await resp.json();
 
       if (!resp.ok) {
@@ -15,7 +32,7 @@ export class HttpClient {
     });
 
   public readonly fetchEmpty = (url: string, options?: RequestInit): Promise<void> =>
-    this.fetch(url, options).then(async (resp) => {
+    this.fetch(url, withJsonContentType(options)).then(async (resp) => {
       if (!resp.ok) {
         throw await resp.json();
       }
diff --git a/test/common/services/HttpClient.test.ts b/test/common/services/HttpClient.test.ts
index b894cd32..ea01faf5 100644
--- a/test/common/services/HttpClient.test.ts
+++ b/test/common/services/HttpClient.test.ts
@@ -14,13 +14,39 @@ describe('HttpClient', () => {
       await expect(httpClient.fetchJson('')).rejects.toEqual(theError);
     });
 
-    it('return json on failure', async () => {
+    it.each([
+      [undefined],
+      [{}],
+      [{ body: undefined }],
+      [{ body: '' }],
+    ])('return json on failure', async (options) => {
       const theJson = { foo: 'bar' };
       fetch.mockResolvedValue({ json: () => theJson, ok: true });
 
-      const result = await httpClient.fetchJson('');
+      const result = await httpClient.fetchJson('the_url', options);
 
       expect(result).toEqual(theJson);
+      expect(fetch).toHaveBeenCalledWith('the_url', options);
+    });
+
+    it.each([
+      [{ body: 'the_body' }],
+      [{
+        body: 'the_body',
+        headers: {
+          'Content-Type': 'text/plain',
+        },
+      }],
+    ])('forwards JSON content-type when appropriate', async (options) => {
+      const theJson = { foo: 'bar' };
+      fetch.mockResolvedValue({ json: () => theJson, ok: true });
+
+      const result = await httpClient.fetchJson('the_url', options);
+
+      expect(result).toEqual(theJson);
+      expect(fetch).toHaveBeenCalledWith('the_url', expect.objectContaining({
+        headers: { 'Content-Type': 'application/json' },
+      }));
     });
   });