diff --git a/lib/octokit.js b/lib/octokit.js
index d1d1baa9..6bb6db1c 100644
--- a/lib/octokit.js
+++ b/lib/octokit.js
@@ -55,7 +55,8 @@ export const SemanticReleaseOctokit = Octokit.plugin(
 export function toOctokitOptions(options) {
   const baseUrl =
     "githubApiUrl" in options && options.githubApiUrl
-      ? options.githubApiUrl
+      ? // Use `urljoin` to normalize the provided URL
+        urljoin(options.githubApiUrl, "")
       : "githubUrl" in options && options.githubUrl
         ? urljoin(options.githubUrl, options.githubApiPathPrefix)
         : undefined;
diff --git a/test/to-octokit-options.test.js b/test/to-octokit-options.test.js
index 30e88973..38c3a4b8 100644
--- a/test/to-octokit-options.test.js
+++ b/test/to-octokit-options.test.js
@@ -52,3 +52,18 @@ test("Do not use a proxy if set to false", async (t) => {
   });
   t.is(request.agent, undefined);
 });
+
+test("githubUrl with trailing slash", async (t) => {
+  const options = toOctokitOptions({
+    githubUrl: "http://localhost:10001/",
+    githubApiPathPrefix: "",
+  });
+  t.is(options.baseUrl, "http://localhost:10001");
+});
+
+test("githubApiUrl with trailing slash", async (t) => {
+  const options = toOctokitOptions({
+    githubApiUrl: "http://api.localhost:10001/",
+  });
+  t.is(options.baseUrl, "http://api.localhost:10001");
+});