diff --git a/app/api/routes/zipcode.py b/app/api/routes/zipcode.py
index e2d7cdb..13fb4af 100644
--- a/app/api/routes/zipcode.py
+++ b/app/api/routes/zipcode.py
@@ -1,4 +1,5 @@
 from fastapi import APIRouter
+from fastapi.exceptions import RequestValidationError
 
 from app.core.errors.base import AppError
 from app.services.external_apis.zipcode_api import ZipCodeAPI
@@ -19,11 +20,26 @@ def lookup_address(address: str):
     Example: 
         address = "1600 Amphitheatre Parkway, Mountain View, CA, US"
     """
+    if not address.strip():
+        raise RequestValidationError(
+            errors=[
+                {
+                    "loc": ("query", "address"),
+                    "msg": "address must not be blank",
+                    "input": address,
+                    "type": "value_error",
+                }
+            ]
+        )
+
     zipcode_api = ZipCodeAPI()
     try:
         return zipcode_api.lookup_address(address)
     except TimeoutError as e:
-        raise AppError(str(e), status_code=504)
+        raise AppError(str(e), status_code=504, error_code="GEOCODING_TIMEOUT")
+    except RuntimeError as e:
+        # Nominatim answered with an error: the failure is upstream, not ours
+        raise AppError(str(e), status_code=502, error_code="GEOCODING_FAILED")
     except Exception as e:
         raise AppError(str(e), status_code=500)
 
diff --git a/tests/test_api.py b/tests/test_api.py
index 3088215..350cf0c 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -635,6 +635,60 @@ def test_forecast_invalid_params_rejected(self, client, monkeypatch, overrides,
         assert body["validation_errors"][0]["field"] == field
 
 
+# ═══════════════════════════════════════════════════════════════════════════
+# Address lookup endpoint
+# ═══════════════════════════════════════════════════════════════════════════
+
+class TestZipcodeEndpoints:
+
+    LOOKUP_URL = f"{API_PREFIX}/zipcode/lookup-address"
+    GEOCODE = "app.services.external_apis.zipcode_api._GEOLOCATOR.geocode"
+
+    @pytest.mark.parametrize("address", ["", "   "])
+    def test_lookup_blank_address_rejected(self, client, monkeypatch, address):
+        def fake_geocode(*args, **kwargs):
+            raise AssertionError("Nominatim should not be called for a blank address")
+
+        monkeypatch.setattr(self.GEOCODE, fake_geocode)
+
+        resp = client.get(self.LOOKUP_URL, params={"address": address})
+        assert resp.status_code == 422
+        body = resp.json()
+        assert body["error_code"] == "VALIDATION_ERROR"
+        assert body["validation_errors"][0]["field"] == "query.address"
+
+    def test_lookup_upstream_error_is_502(self, client, monkeypatch):
+        from geopy.exc import GeocoderServiceError
+
+        def fake_geocode(*args, **kwargs):
+            raise GeocoderServiceError("HTTP Error 503: Service Unavailable")
+
+        monkeypatch.setattr(self.GEOCODE, fake_geocode)
+
+        resp = client.get(self.LOOKUP_URL, params={"address": "Paris"})
+        assert resp.status_code == 502
+        assert resp.json()["error_code"] == "GEOCODING_FAILED"
+
+    def test_lookup_timeout_is_504(self, client, monkeypatch):
+        from geopy.exc import GeocoderTimedOut
+
+        def fake_geocode(*args, **kwargs):
+            raise GeocoderTimedOut("timed out")
+
+        monkeypatch.setattr(self.GEOCODE, fake_geocode)
+
+        resp = client.get(self.LOOKUP_URL, params={"address": "Paris"})
+        assert resp.status_code == 504
+        assert resp.json()["error_code"] == "GEOCODING_TIMEOUT"
+
+    def test_lookup_no_results(self, client, monkeypatch):
+        monkeypatch.setattr(self.GEOCODE, lambda *args, **kwargs: None)
+
+        resp = client.get(self.LOOKUP_URL, params={"address": "Nowhere at all"})
+        assert resp.status_code == 200
+        assert resp.json() == []
+
+
 # ═══════════════════════════════════════════════════════════════════════════
 # End-to-end pipeline
 # ═══════════════════════════════════════════════════════════════════════════