diff --git a/CHANGES.md b/CHANGES.md
index e1ea698..b7d1a33 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -23,6 +23,7 @@
 
 #### Minor Fixes and Improvements
 
+ - [#400](https://github.com/Day8/re-frame/pull/400) Improve error message when a registered cofx can't be found
  - The effect handler for `:dispatch-n` will now ignore `nils`. [See checkin](https://github.com/Day8/re-frame/commit/6efdae438f393f8121a2d6dfbf76db00e6dafbf5)
  - [#340](https://github.com/Day8/re-frame/pull/340)
  - [#341](https://github.com/Day8/re-frame/pull/341) Fix `re-frame.core/on-changes` to work even if event handler does not set `:db`. 
diff --git a/docs/CodeWalkthrough.md b/docs/CodeWalkthrough.md
index 0ed40ed..6517753 100644
--- a/docs/CodeWalkthrough.md
+++ b/docs/CodeWalkthrough.md
@@ -62,7 +62,7 @@ informal description, and here it is ... for this app `app-db` will contain
 a two-key map like this:
 ```cljs
 {:time       (js/Date.)  ;; current time for display
- :time-color "#f88"}     ;; the colour in which the time should be be shown
+ :time-color "#f88"}     ;; the colour in which the time should be shown
 ```
 
 re-frame itself owns/manages `app-db` (see FAQ #1), and it will
diff --git a/src/re_frame/cofx.cljc b/src/re_frame/cofx.cljc
index 9b1ecab..ec2668d 100644
--- a/src/re_frame/cofx.cljc
+++ b/src/re_frame/cofx.cljc
@@ -83,13 +83,17 @@
     :id      :coeffects
     :before  (fn coeffects-before
                [context]
-               (update context :coeffects (get-handler kind id)))))
+               (if-let [handler (get-handler kind id)]
+                 (update context handler :coeffects)
+                 (console :error "No cofx handler registered for \"" id "\"")))))
   ([id value]
    (->interceptor
      :id     :coeffects
      :before  (fn coeffects-before
                 [context]
-                (update context :coeffects (get-handler kind id) value)))))
+                (if-let [handler (get-handler kind id)]
+                  (update context :coeffects handler value)
+                  (console :error "No cofx handler registered for \"" id "\""))))))
 
 
 ;; -- Builtin CoEffects Handlers  ---------------------------------------------