diff --git a/npm_install.py b/npm_install.py
index ecf8893..7e80d02 100644
--- a/npm_install.py
+++ b/npm_install.py
@@ -573,7 +573,6 @@ def adjust_nginx_like_paths_in_tree(root: Path):
         cand.write_text(txt, encoding="utf-8")
 
 def install_node_and_yarn(node_pkg: str):
-    # Node
     apt_install([node_pkg])
     if shutil.which("yarn") or shutil.which("yarnpkg"):
         return
@@ -584,24 +583,44 @@ def install_node_and_yarn(node_pkg: str):
         os.symlink("/usr/bin/yarnpkg","/usr/bin/yarn")
 
 def _build_frontend(src_frontend: Path, dest_frontend: Path):
-
     def _semver(s: str) -> bool:
         return bool(re.match(r"^\d+(?:\.\d+){1,3}$", (s or "").strip()))
 
-    def _good_yarn(cmd: str) -> bool:
-        v = (run_out([cmd, "--version"], check=False) or "").strip()
+    def _good_yarn(argv: list[str]) -> bool:
+        v = (run_out(argv + ["--version"], check=False) or "").strip()
         return _semver(v)
 
-    yarn_cmd = None
-    if shutil.which("yarn") and _good_yarn("yarn"):
-        yarn_cmd = ["yarn"]
-    elif shutil.which("yarnpkg") and _good_yarn("yarnpkg"):
-        yarn_cmd = ["yarnpkg"]
-    elif shutil.which("npm"):
-        if (run_out(["npm", "--version"], check=False) or "").strip():
-            yarn_cmd = ["npm", "exec", "--yes", "yarn@stable"]
+    def _pick_yarn_cmd() -> list[str] | None:
+        for c in (["yarn"], ["yarnpkg"]):
+            if shutil.which(c[0]) and _good_yarn(c):
+                return c
+        if shutil.which("npm") and (run_out(["npm", "--version"], check=False) or "").strip():
+            if _good_yarn(["npm", "exec", "--yes", "yarn@stable"]):
+                return ["npm", "exec", "--yes", "yarn@stable"]
+        if shutil.which("npx") and (run_out(["npx", "--version"], check=False) or "").strip():
+            if _good_yarn(["npx", "-y", "yarn@stable"]):
+                return ["npx", "-y", "yarn@stable"]
+        return None
+
+    def _ensure_yarn_installed():
+        if not shutil.which("npm"):
+            try:
+                apt_try_install(["npm"])
+            except Exception:
+                run(["apt-get", "update"], check=False)
+                run(["apt-get", "install", "-y", "npm"])
+        run(["npm", "install", "-g", "yarn"], check=False)
+
+    yarn_cmd = _pick_yarn_cmd()
     if not yarn_cmd:
-        raise RuntimeError("No yarn in system")
+        _ensure_yarn_installed()
+        yarn_cmd = _pick_yarn_cmd()
+
+    if not yarn_cmd:
+        raise RuntimeError(
+            "Unable to detect or install a valid Yarn. "
+            "Try: apt-get install -y npm && npm i -g yarn."
+        )
 
     with step("Installing frontend dependencies (yarn)"):
         os.environ["NODE_ENV"] = "development"
@@ -612,7 +631,6 @@ def _build_frontend(src_frontend: Path, dest_frontend: Path):
             Path(cache_dir).mkdir(parents=True, exist_ok=True)
 
         run(yarn_cmd + ["cache", "clean"], check=False)
-
         run(yarn_cmd + ["install"])
 
     with step("Building frontend (yarn build)"):
@@ -625,6 +643,7 @@ def _build_frontend(src_frontend: Path, dest_frontend: Path):
         if (src_frontend / "app-images").exists():
             shutil.copytree(src_frontend / "app-images", dest_frontend / "images", dirs_exist_ok=True)
 
+
 def patch_npm_backend_commands():
     candidates = [
         Path("/opt/npm/lib/utils.js"),