diff --git a/dist/index.js b/dist/index.js
index a16648d..71893ad 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -3872,10 +3872,17 @@ async function getChangesSinceMergeBase(baseRef, ref, initialFetchDepth) {
     let noMergeBase = false;
     core.startGroup(`Searching for merge-base ${baseRef}...${ref}`);
     try {
+        let init = true;
         let lastCommitCount = await getCommitCount();
         let depth = Math.max(lastCommitCount * 2, initialFetchDepth);
         while (!(await hasMergeBase())) {
-            await exec_1.default('git', ['fetch', `--depth=${depth}`, 'origin', `${baseRef}:${baseRef}`, `${ref}`]);
+            if (init) {
+                await exec_1.default('git', ['fetch', `--depth=${depth}`, 'origin', `${baseRef}:${baseRef}`, `${ref}`]);
+                init = false;
+            }
+            else {
+                await exec_1.default('git', ['fetch', `--deepen=${depth}`, 'origin', baseRef, ref]);
+            }
             const commitCount = await getCommitCount();
             if (commitCount === lastCommitCount) {
                 core.info('No more commits were fetched');
diff --git a/src/git.ts b/src/git.ts
index c58621f..a55faa6 100644
--- a/src/git.ts
+++ b/src/git.ts
@@ -66,10 +66,16 @@ export async function getChangesSinceMergeBase(
   let noMergeBase = false
   core.startGroup(`Searching for merge-base ${baseRef}...${ref}`)
   try {
+    let init = true
     let lastCommitCount = await getCommitCount()
     let depth = Math.max(lastCommitCount * 2, initialFetchDepth)
     while (!(await hasMergeBase())) {
-      await exec('git', ['fetch', `--depth=${depth}`, 'origin', `${baseRef}:${baseRef}`, `${ref}`])
+      if (init) {
+        await exec('git', ['fetch', `--depth=${depth}`, 'origin', `${baseRef}:${baseRef}`, `${ref}`])
+        init = false
+      } else {
+        await exec('git', ['fetch', `--deepen=${depth}`, 'origin', baseRef, ref])
+      }
       const commitCount = await getCommitCount()
       if (commitCount === lastCommitCount) {
         core.info('No more commits were fetched')