diff --git a/src/tbd/core.clj b/src/tbd/core.clj
index f5e1388..cb01456 100644
--- a/src/tbd/core.clj
+++ b/src/tbd/core.clj
@@ -10,6 +10,17 @@
             [tbd.health.routes :as health]
             [tbd.math.routes :as math]))
 
+(defn- swagger-handler
+  "reitit emits `\"definitions\": null` when no route declares a schema, which
+  violates the Swagger 2.0 schema (must be an object) and makes validators reject the spec."
+  []
+  (let [handler (swagger/create-swagger-handler)]
+    (fn [req]
+      (let [resp (handler req)]
+        (cond-> resp
+          (and (map? (:body resp)) (nil? (:definitions (:body resp))))
+          (update :body dissoc :definitions))))))
+
 ;; Each logical group (health, users, orders, ...) owns a `tbd.<group>.routes`
 ;; namespace that returns its own route subtree; they're concatenated here.
 (def router
@@ -17,7 +28,7 @@
     [["/swagger.json"
       {:get {:no-doc true
              :swagger {:info {:title "tbd API" :version "1.0.0"}}
-             :handler (swagger/create-swagger-handler)}}]
+             :handler (swagger-handler)}}]
      ["/" {:get {:no-doc true
                  :handler (fn [_req]
                             {:status 200
diff --git a/test/tbd/core_test.clj b/test/tbd/core_test.clj
index b301fb7..1ec5680 100644
--- a/test/tbd/core_test.clj
+++ b/test/tbd/core_test.clj
@@ -22,7 +22,9 @@
 (deftest swagger-spec-test
   (let [resp (request :get "/swagger.json")]
     (is (= 200 (:status resp)))
-    (is (re-find #"/api/ping" (slurp (:body resp))))))
+    (is (re-find #"/api/ping" (slurp (:body resp))))
+    (is (not (re-find #"\"definitions\":null" (slurp (:body (request :get "/swagger.json")))))
+        "a null `definitions` makes the spec invalid Swagger 2.0")))
 
 (deftest unknown-route-test
   (is (= 404 (:status (request :get "/nope")))))