diff --git a/synapse/appservice/__init__.py b/synapse/appservice/__init__.py
index 6ee5240c4e..a0971e3c48 100644
--- a/synapse/appservice/__init__.py
+++ b/synapse/appservice/__init__.py
@@ -88,6 +88,7 @@ class ApplicationService:
         supports_ephemeral: bool = False,
         msc3202_transaction_extensions: bool = False,
         msc4190_device_management: bool = False,
+        supports_profile_lookup: bool = False,
     ):
         self.token = token
         self.url = (
@@ -100,6 +101,7 @@ class ApplicationService:
         self.id = id
         self.ip_range_whitelist = ip_range_whitelist
         self.supports_ephemeral = supports_ephemeral
+        self.supports_profile_lookup = supports_profile_lookup
         self.msc3202_transaction_extensions = msc3202_transaction_extensions
         self.msc4190_device_management = msc4190_device_management
 
diff --git a/synapse/appservice/api.py b/synapse/appservice/api.py
index 2c24db0822..fc9cb06c0e 100644
--- a/synapse/appservice/api.py
+++ b/synapse/appservice/api.py
@@ -278,7 +278,7 @@ class ApplicationServiceApi(SimpleHttpClient):
             url = f"{service.url}{APP_SERVICE_PREFIX}/profile/{urllib.parse.quote(user_id)}"
 
             if key:
-                url += f"/{key}"
+                url += f"/{urllib.parse.quote(key)}"
 
             response = await self.get_json(
                 url,
diff --git a/synapse/config/appservice.py b/synapse/config/appservice.py
index dda6bcd1b7..68816cd85e 100644
--- a/synapse/config/appservice.py
+++ b/synapse/config/appservice.py
@@ -171,6 +171,7 @@ def _load_appservice(
         ip_range_whitelist = IPSet(as_info.get("ip_range_whitelist"))
 
     supports_ephemeral = as_info.get("de.sorunome.msc2409.push_ephemeral", False)
+    lookup_profiles = as_info.get("uk.half-shot.lookup_profile", False)
 
     # Opt-in flag for the MSC3202-specific transactional behaviour.
     # When enabled, appservice transactions contain the following information:
@@ -206,6 +207,7 @@ def _load_appservice(
         rate_limited=rate_limited,
         ip_range_whitelist=ip_range_whitelist,
         supports_ephemeral=supports_ephemeral,
+        supports_profile_lookup=lookup_profiles,
         msc3202_transaction_extensions=msc3202_transaction_extensions,
         msc4190_device_management=msc4190_enabled,
     )
diff --git a/synapse/handlers/appservice.py b/synapse/handlers/appservice.py
index d2a39ba151..f101c671f0 100644
--- a/synapse/handlers/appservice.py
+++ b/synapse/handlers/appservice.py
@@ -724,11 +724,12 @@ class ApplicationServicesHandler:
         user_query_services = self._get_services_for_user(user_id=user_id)
         accumulated_profile = {}
         for user_service in user_query_services:
-            profile = await self.appservice_api.query_profile(
-                user_service, user_id, from_user_id, key
-            )
-            if profile:
-                accumulated_profile.update(profile)
+            if user_service.supports_profile_lookup:
+                profile = await self.appservice_api.query_profile(
+                    user_service, user_id, from_user_id, key
+                )
+                if profile:
+                    accumulated_profile.update(profile)
         return accumulated_profile
 
     async def query_room_alias_exists(