diff --git a/hermes_cli/main.py b/hermes_cli/main.py
index 57ab222bf0..66e8b9d815 100644
--- a/hermes_cli/main.py
+++ b/hermes_cli/main.py
@@ -789,6 +789,14 @@ def cmd_update(args):
         print("  curl -fsSL https://raw.githubusercontent.com/NousResearch/hermes-agent/main/scripts/install.sh | bash")
         sys.exit(1)
     
+    # On Windows, git can fail with "unable to write loose object file: Invalid argument"
+    # due to filesystem atomicity issues. Set the recommended workaround.
+    if sys.platform == "win32":
+        subprocess.run(
+            ["git", "config", "windows.appendAtomically", "false"],
+            cwd=PROJECT_ROOT, check=False, capture_output=True
+        )
+
     # Fetch and pull
     try:
         print("→ Fetching updates...")
@@ -832,7 +840,7 @@ def cmd_update(args):
                 env={**os.environ, "VIRTUAL_ENV": str(PROJECT_ROOT / "venv")}
             )
         else:
-            venv_pip = PROJECT_ROOT / "venv" / "bin" / "pip"
+            venv_pip = PROJECT_ROOT / "venv" / ("Scripts" if sys.platform == "win32" else "bin") / "pip"
             if venv_pip.exists():
                 subprocess.run([str(venv_pip), "install", "-e", ".", "--quiet"], cwd=PROJECT_ROOT, check=True)
             else:
diff --git a/scripts/install.ps1 b/scripts/install.ps1
index b4e9758fe1..c5c7789e0e 100644
--- a/scripts/install.ps1
+++ b/scripts/install.ps1
@@ -462,9 +462,13 @@ function Install-Repository {
         }
     }
     
+    # Fix Windows git "unable to write loose object file" error.
+    # Must be set before any git operations that write objects.
+    Push-Location $InstallDir
+    git config windows.appendAtomically false
+
     # Ensure submodules are initialized and updated
     Write-Info "Initializing submodules (mini-swe-agent, tinker-atropos)..."
-    Push-Location $InstallDir
     git submodule update --init --recursive
     Pop-Location
     Write-Success "Submodules ready"