diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 3aa5fc9..fe2539f 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -165,6 +165,22 @@ jobs:
       - name: Verify submodules recursive
         run: __test__/verify-submodules-recursive.sh
 
+      # Worktree credentials
+      - name: Checkout for worktree test
+        uses: ./
+        with:
+          path: worktree-test
+      - name: Verify worktree credentials
+        shell: bash
+        run: __test__/verify-worktree.sh worktree-test worktree-branch
+
+      # Worktree credentials in container step
+      - name: Verify worktree credentials in container step
+        if: runner.os == 'Linux'
+        uses: docker://bitnami/git:latest
+        with:
+          args: bash __test__/verify-worktree.sh worktree-test container-worktree-branch
+
       # Basic checkout using REST API
       - name: Remove basic
         if: runner.os != 'windows'
diff --git a/__test__/verify-worktree.sh b/__test__/verify-worktree.sh
new file mode 100755
index 0000000..3a4d3e4
--- /dev/null
+++ b/__test__/verify-worktree.sh
@@ -0,0 +1,51 @@
+#!/bin/bash
+set -e
+
+# Verify worktree credentials
+# This test verifies that git credentials work in worktrees created after checkout
+# Usage: verify-worktree.sh <checkout-path> <worktree-name>
+
+CHECKOUT_PATH="$1"
+WORKTREE_NAME="$2"
+
+if [ -z "$CHECKOUT_PATH" ] || [ -z "$WORKTREE_NAME" ]; then
+  echo "Usage: verify-worktree.sh <checkout-path> <worktree-name>"
+  exit 1
+fi
+
+cd "$CHECKOUT_PATH"
+
+# Add safe directory for container environments
+git config --global --add safe.directory "*" 2>/dev/null || true
+
+# Show the includeIf configuration
+echo "Git config includeIf entries:"
+git config --list --show-origin | grep -i include || true
+
+# Create the worktree
+echo "Creating worktree..."
+git worktree add "../$WORKTREE_NAME" HEAD --detach
+
+# Change to worktree directory
+cd "../$WORKTREE_NAME"
+
+# Verify we're in a worktree
+echo "Verifying worktree gitdir:"
+cat .git
+
+# Verify credentials are available in worktree by checking extraheader is configured
+echo "Checking credentials in worktree..."
+if git config --list --show-origin | grep -q "extraheader"; then
+  echo "Credentials are configured in worktree"
+else
+  echo "ERROR: Credentials are NOT configured in worktree"
+  echo "Full git config:"
+  git config --list --show-origin
+  exit 1
+fi
+
+# Verify fetch works in the worktree
+echo "Fetching in worktree..."
+git fetch origin
+
+echo "Worktree credentials test passed!"
diff --git a/dist/index.js b/dist/index.js
index a251a19..b9b34d3 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -412,6 +412,9 @@ class GitAuthHelper {
                 // Configure host includeIf
                 const hostIncludeKey = `includeIf.gitdir:${gitDir}.path`;
                 yield this.git.config(hostIncludeKey, credentialsConfigPath);
+                // Configure host includeIf for worktrees
+                const hostWorktreeIncludeKey = `includeIf.gitdir:${gitDir}/worktrees/*.path`;
+                yield this.git.config(hostWorktreeIncludeKey, credentialsConfigPath);
                 // Container git directory
                 const workingDirectory = this.git.getWorkingDirectory();
                 const githubWorkspace = process.env['GITHUB_WORKSPACE'];
@@ -424,6 +427,9 @@ class GitAuthHelper {
                 // Configure container includeIf
                 const containerIncludeKey = `includeIf.gitdir:${containerGitDir}.path`;
                 yield this.git.config(containerIncludeKey, containerCredentialsPath);
+                // Configure container includeIf for worktrees
+                const containerWorktreeIncludeKey = `includeIf.gitdir:${containerGitDir}/worktrees/*.path`;
+                yield this.git.config(containerWorktreeIncludeKey, containerCredentialsPath);
             }
         });
     }
diff --git a/src/git-auth-helper.ts b/src/git-auth-helper.ts
index a1950a6..e67db14 100644
--- a/src/git-auth-helper.ts
+++ b/src/git-auth-helper.ts
@@ -374,6 +374,10 @@ class GitAuthHelper {
       const hostIncludeKey = `includeIf.gitdir:${gitDir}.path`
       await this.git.config(hostIncludeKey, credentialsConfigPath)
 
+      // Configure host includeIf for worktrees
+      const hostWorktreeIncludeKey = `includeIf.gitdir:${gitDir}/worktrees/*.path`
+      await this.git.config(hostWorktreeIncludeKey, credentialsConfigPath)
+
       // Container git directory
       const workingDirectory = this.git.getWorkingDirectory()
       const githubWorkspace = process.env['GITHUB_WORKSPACE']
@@ -395,6 +399,13 @@ class GitAuthHelper {
       // Configure container includeIf
       const containerIncludeKey = `includeIf.gitdir:${containerGitDir}.path`
       await this.git.config(containerIncludeKey, containerCredentialsPath)
+
+      // Configure container includeIf for worktrees
+      const containerWorktreeIncludeKey = `includeIf.gitdir:${containerGitDir}/worktrees/*.path`
+      await this.git.config(
+        containerWorktreeIncludeKey,
+        containerCredentialsPath
+      )
     }
   }