diff --git a/setup-flutter/action.yml b/setup-flutter/action.yml
index 1131575..d7c3c2f 100644
--- a/setup-flutter/action.yml
+++ b/setup-flutter/action.yml
@@ -45,13 +45,22 @@ runs:
       if: runner.os != 'Windows' && steps.flutter-cache.outputs.cache-hit != 'true'
       shell: bash
       run: |
+        LOCK_DIR="${TMPDIR:-/tmp}/flutter-sdk-setup.lock"
+        for i in {1..60}; do
+          if mkdir "$LOCK_DIR" 2>/dev/null; then
+            break
+          fi
+          echo "Waiting for concurrent Flutter setup lock ($i/60)..."
+          sleep 2
+        done
+
         SDK_DIR="$HOME/flutter-sdk"
         CLONE_URL="${{ inputs.mirror_url }}"
         if [ -n "${{ inputs.git_token }}" ] && [[ "$CLONE_URL" == https://* ]]; then
           CLONE_URL="https://git:${{ inputs.git_token }}@${CLONE_URL#https://}"
         fi
 
-        if [ ! -d "$SDK_DIR/.git" ]; then
+        if [ ! -d "$SDK_DIR/.git" ] || [ ! -f "$SDK_DIR/bin/flutter" ]; then
           echo "Cloning Flutter ${{ inputs.version }} from $CLONE_URL to $SDK_DIR..."
           rm -rf "$SDK_DIR"
           git clone --depth 1 --branch ${{ inputs.version }} "$CLONE_URL" "$SDK_DIR" || {
@@ -59,15 +68,28 @@ runs:
             git clone --depth 1 --branch ${{ inputs.version }} https://github.com/flutter/flutter.git "$SDK_DIR"
           }
         else
-          echo "Updating existing Flutter SDK at $SDK_DIR..."
-          git -C "$SDK_DIR" fetch origin ${{ inputs.version }} --depth=1
-          git -C "$SDK_DIR" reset --hard origin/${{ inputs.version }}
+          echo "Flutter SDK already present at $SDK_DIR. Ready to use."
         fi
 
+        rm -rf "$LOCK_DIR" || true
+
     - name: Install Flutter (Windows)
       if: runner.os == 'Windows' && steps.flutter-cache.outputs.cache-hit != 'true'
       shell: powershell
       run: |
+        $lockDir = Join-Path $env:TEMP "flutter-sdk-setup.lock"
+        $waited = 0
+        while ($true) {
+          try {
+            [System.IO.Directory]::CreateDirectory($lockDir) | Out-Null
+            break
+          } catch {
+            Start-Sleep -Seconds 2
+            $waited += 2
+            if ($waited -ge 120) { break }
+          }
+        }
+
         $sdkDir = "C:\flutter-sdk"
         $cloneUrl = "${{ inputs.mirror_url }}"
         if ("${{ inputs.git_token }}" -ne "" -and $cloneUrl.StartsWith("https://")) {
@@ -83,9 +105,11 @@ runs:
             git clone --depth 1 --branch ${{ inputs.version }} https://github.com/flutter/flutter.git $sdkDir
           }
         } else {
-          echo "Updating existing Flutter SDK at $sdkDir..."
-          git -C $sdkDir fetch origin ${{ inputs.version }} --depth=1
-          git -C $sdkDir reset --hard origin/${{ inputs.version }}
+          echo "Flutter SDK already present at $sdkDir. Ready to use."
+        }
+
+        if (Test-Path $lockDir) {
+          try { [System.IO.Directory]::Delete($lockDir, $true) } catch {}
         }
 
     - name: Add to PATH and Configure (macOS / Linux)