diff --git a/lib/platform/github/index.ts b/lib/platform/github/index.ts
index 54ca05b44b47f036b5f1bbb73f606449b95dfede..3b6c1a81463dadcda7c9126f2eedc6fadd41f716 100644
--- a/lib/platform/github/index.ts
+++ b/lib/platform/github/index.ts
@@ -258,7 +258,6 @@ export async function initRepo({
     }
     // Use default branch as PR target unless later overridden.
     config.defaultBranch = repo.defaultBranchRef.name;
-    config.defaultBranchSha = repo.defaultBranchRef.target.oid;
     // Base branch may be configured but defaultBranch is always fixed
     logger.debug(`${repository} default branch = ${config.defaultBranch}`);
     // GitHub allows administrators to block certain types of merge, so we need to check it
@@ -344,14 +343,6 @@ export async function initRepo({
         { repository_fork: config.repository },
         'Found existing fork'
       );
-      // Need to update base branch
-      logger.debug(
-        {
-          defaultBranch: config.defaultBranch,
-          defaultBranchSha: config.defaultBranchSha,
-        },
-        'Setting defaultBranch ref in fork'
-      );
       // This is a lovely "hack" by GitHub that lets us force update our fork's master
       // with the base commit from the parent repository
       try {
@@ -362,7 +353,7 @@ export async function initRepo({
           `repos/${config.repository}/git/refs/heads/${config.defaultBranch}`,
           {
             body: {
-              sha: config.defaultBranchSha,
+              sha: repo.defaultBranchRef.target.oid,
               force: true,
             },
             token: forkToken || opts.token,
diff --git a/lib/platform/github/types.ts b/lib/platform/github/types.ts
index d2e868c1f19c89956f3aca204990279bb03b4ed0..fe009d192385797940c86ba07228388da225a07e 100644
--- a/lib/platform/github/types.ts
+++ b/lib/platform/github/types.ts
@@ -56,7 +56,6 @@ export interface LocalRepoConfig {
   issueList: any[] | null;
   mergeMethod: string;
   defaultBranch: string;
-  defaultBranchSha?: string;
   repositoryOwner: string;
   repository: string | null;
   localDir: string;