diff --git a/l4d2web/services/l4d2_facade.py b/l4d2web/services/l4d2_facade.py
index eaf8c21..80e9e8d 100644
--- a/l4d2web/services/l4d2_facade.py
+++ b/l4d2web/services/l4d2_facade.py
@@ -44,11 +44,16 @@ def build_server_spec_payload(
         for overlay_id, _, expose in reversed(overlay_rows)
         if expose
     ]
+    config_lines: list[str] = exec_lines + json.loads(blueprint.config)
+    # rcon_password is appended LAST so neither overlays nor user blueprint
+    # config can override it (Source's cvar semantics are last-wins).
+    if server.rcon_password:
+        config_lines.append(f'rcon_password "{server.rcon_password}"')
     return {
         "port": server.port,
         "overlays": overlays,
         "arguments": json.loads(blueprint.arguments),
-        "config": exec_lines + json.loads(blueprint.config),
+        "config": config_lines,
     }
 
 
diff --git a/l4d2web/tests/test_l4d2_facade.py b/l4d2web/tests/test_l4d2_facade.py
index 60ad3a6..c5e20c8 100644
--- a/l4d2web/tests/test_l4d2_facade.py
+++ b/l4d2web/tests/test_l4d2_facade.py
@@ -343,3 +343,45 @@ def test_initialize_fails_fast_on_uncached_workshop_items(
     assert all("initialize" not in cmd for cmd in invocations), invocations
 
 
+# ---------------------------------------------------------------------------
+# build_server_spec_payload — rcon_password injection
+# ---------------------------------------------------------------------------
+
+def _make_server_blueprint(rcon: str = "") -> tuple[Server, Blueprint]:
+    bp = Blueprint(
+        id=1, user_id=1, name="bp",
+        arguments='["-tickrate","60"]',
+        config='["sv_consistency 1","mp_gamemode coop"]',
+    )
+    srv = Server(
+        id=1, user_id=1, blueprint_id=1, name="s", port=27500,
+        rcon_password=rcon,
+    )
+    return srv, bp
+
+
+def test_build_server_spec_payload_appends_rcon_password_last() -> None:
+    from l4d2web.services.l4d2_facade import build_server_spec_payload
+
+    srv, bp = _make_server_blueprint(rcon="topsecret123")
+    overlays = [(7, "/overlays/7", True), (8, "/overlays/8", False)]
+    spec = build_server_spec_payload(srv, bp, overlays)
+
+    cfg = spec["config"]
+    # rcon_password line is the LAST entry — overlay exec lines + blueprint
+    # config + rcon_password.
+    assert cfg[-1] == 'rcon_password "topsecret123"'
+    # Lines before our injection still contain the blueprint config.
+    assert "sv_consistency 1" in cfg
+    assert "mp_gamemode coop" in cfg
+
+
+def test_build_server_spec_payload_omits_rcon_password_when_empty() -> None:
+    from l4d2web.services.l4d2_facade import build_server_spec_payload
+
+    srv, bp = _make_server_blueprint(rcon="")
+    spec = build_server_spec_payload(srv, bp, [])
+    for line in spec["config"]:
+        assert not line.startswith("rcon_password ")
+
+