diff --git a/backend/routers/updates.py b/backend/routers/updates.py
index c0f6a81..f60cf4f 100644
--- a/backend/routers/updates.py
+++ b/backend/routers/updates.py
@@ -147,26 +147,45 @@ def _parse_apt_packages(install_sh_content: str) -> set[str]:
 
 
 async def _get_installed_packages(packages: set[str]) -> set[str]:
-    """Check which packages from the set are already installed via dpkg."""
+    """Check which packages from the set are already installed via dpkg-query."""
     if not packages:
         return set()
     installed = set()
-    for pkg in packages:
+    # Use dpkg-query for batch check — more reliable than dpkg -s
+    # Note: dpkg-query returns non-zero if ANY package is unknown, but still
+    # outputs status for known packages on stdout.
+    try:
         proc = await asyncio.create_subprocess_exec(
-            "dpkg", "-s", pkg,
+            "dpkg-query", "-W", "-f", "${Package} ${Status}\n", *sorted(packages),
             stdout=asyncio.subprocess.PIPE,
             stderr=asyncio.subprocess.PIPE,
             env=_safe_env(),
         )
-        try:
-            stdout, _ = await asyncio.wait_for(proc.communicate(), timeout=5)
-        except asyncio.TimeoutError:
-            continue
-        if proc.returncode == 0:
-            # Verify it's actually installed (Status: install ok installed)
-            output = stdout.decode()
-            if "Status:" in output and "installed" in output:
-                installed.add(pkg)
+        stdout, _ = await asyncio.wait_for(proc.communicate(), timeout=10)
+        # returncode may be non-zero if some packages are unknown — that's fine
+        for line in stdout.decode().strip().splitlines():
+            # Format: "packagename install ok installed"
+            if "install ok installed" in line:
+                pkg_name = line.split()[0]
+                installed.add(pkg_name)
+    except (asyncio.TimeoutError, Exception) as e:
+        log.debug("dpkg-query failed, falling back to individual checks: %s", e)
+        # Fallback: check each package individually
+        for pkg in packages:
+            proc = await asyncio.create_subprocess_exec(
+                "dpkg", "-s", pkg,
+                stdout=asyncio.subprocess.PIPE,
+                stderr=asyncio.subprocess.PIPE,
+                env=_safe_env(),
+            )
+            try:
+                stdout, _ = await asyncio.wait_for(proc.communicate(), timeout=5)
+            except asyncio.TimeoutError:
+                continue
+            if proc.returncode == 0:
+                output = stdout.decode()
+                if "install ok installed" in output:
+                    installed.add(pkg)
     return installed
 
 
@@ -262,6 +281,20 @@ async def install_deps(req: InstallDepsRequest, _user: str = Depends(get_current
             raise HTTPException(400, f"Invalid package name: {pkg}")
 
     apt_bin = shutil.which("apt-get") or "/usr/bin/apt-get"
+
+    # Update package lists first
+    log.info("Running apt-get update before install")
+    update_proc = await asyncio.create_subprocess_exec(
+        apt_bin, "update", "-qq",
+        stdout=asyncio.subprocess.PIPE,
+        stderr=asyncio.subprocess.PIPE,
+        env=_safe_env(),
+    )
+    try:
+        await asyncio.wait_for(update_proc.communicate(), timeout=120)
+    except asyncio.TimeoutError:
+        pass  # Non-fatal, proceed with install anyway
+
     cmd = [apt_bin, "install", "-y"] + req.packages
     log.info("Installing system packages: %s", " ".join(req.packages))
 
diff --git a/install.sh b/install.sh
index f9ba294..a5e9c42 100755
--- a/install.sh
+++ b/install.sh
@@ -52,6 +52,7 @@ install_deps() {
         xdotool \
         imagemagick \
         x11-utils \
+        libxcb-cursor0 \
         > /dev/null 2>&1
     ok "System dependencies installed."
 }