diff --git a/decnet/web/router/topology/api_catalog.py b/decnet/web/router/topology/api_catalog.py
index 44c44114..728f26a8 100644
--- a/decnet/web/router/topology/api_catalog.py
+++ b/decnet/web/router/topology/api_catalog.py
@@ -30,6 +30,7 @@ router = APIRouter()
     tags=["MazeNET Topologies"],
     response_model=ServiceCatalogResponse,
     responses={
+        400: {"description": "Malformed query parameters"},
         401: {"description": "Missing or invalid credentials"},
         403: {"description": "Insufficient permissions"},
     },
@@ -70,6 +71,7 @@ async def api_next_subnet(
     tags=["MazeNET Topologies"],
     response_model=NextIPResponse,
     responses={
+        400: {"description": "Malformed path parameters"},
         401: {"description": "Missing or invalid credentials"},
         403: {"description": "Insufficient permissions"},
         404: {"description": "Topology or LAN not found"},
diff --git a/decnet/web/router/topology/api_get_topology.py b/decnet/web/router/topology/api_get_topology.py
index dd9ebaa9..11a1535b 100644
--- a/decnet/web/router/topology/api_get_topology.py
+++ b/decnet/web/router/topology/api_get_topology.py
@@ -23,6 +23,7 @@ router = APIRouter()
     tags=["MazeNET Topologies"],
     response_model=TopologyDetail,
     responses={
+        400: {"description": "Malformed path parameters"},
         401: {"description": "Missing or invalid credentials"},
         403: {"description": "Insufficient permissions"},
         404: {"description": "Topology not found"},
@@ -49,6 +50,7 @@ async def api_get_topology(
     tags=["MazeNET Topologies"],
     response_model=list[TopologyStatusEventRow],
     responses={
+        400: {"description": "Malformed query parameters"},
         401: {"description": "Missing or invalid credentials"},
         403: {"description": "Insufficient permissions"},
         404: {"description": "Topology not found"},
diff --git a/decnet/web/router/topology/api_list_topologies.py b/decnet/web/router/topology/api_list_topologies.py
index f1df8ab3..af97c90f 100644
--- a/decnet/web/router/topology/api_list_topologies.py
+++ b/decnet/web/router/topology/api_list_topologies.py
@@ -17,6 +17,7 @@ router = APIRouter()
     tags=["MazeNET Topologies"],
     response_model=TopologyListResponse,
     responses={
+        400: {"description": "Malformed query parameters"},
         401: {"description": "Missing or invalid credentials"},
         403: {"description": "Insufficient permissions"},
     },