diff --git a/modules/reitit-core/src/reitit/exception.cljc b/modules/reitit-core/src/reitit/exception.cljc
index 5eb6e524..81a6c693 100644
--- a/modules/reitit-core/src/reitit/exception.cljc
+++ b/modules/reitit-core/src/reitit/exception.cljc
@@ -7,11 +7,14 @@
   ([type data]
    (throw (ex-info (str type) {:type type, :data data}))))
 
+(defn get-message [e]
+  #?(:clj (.getMessage ^Exception e) :cljs (ex-message e)))
+
 (defmulti format-exception (fn [type _ _] type))
 
 (defn exception [e]
   (let [data (ex-data e)
-        message (format-exception (:type data) #?(:clj (.getMessage ^Exception e) :cljs (ex-message e)) (:data data))]
+        message (format-exception (:type data) (get-message e) (:data data))]
     ;; there is a 3-arity version (+cause) of ex-info, but the default repl error message is taken from the cause
     (ex-info message (assoc (or data {}) ::cause e))))
 
@@ -35,3 +38,6 @@
            (fn [[name vals]]
              (str name "\n-> " (str/join "\n-> " (mapv first vals)) "\n"))
            conflicts)))
+
+(defmethod format-exception :reitit.impl/merge-data [_ _ data]
+  (str "Error merging route-data\n\n" (pr-str data)))
diff --git a/modules/reitit-core/src/reitit/impl.cljc b/modules/reitit-core/src/reitit/impl.cljc
index 8797b77b..b2aeb250 100644
--- a/modules/reitit-core/src/reitit/impl.cljc
+++ b/modules/reitit-core/src/reitit/impl.cljc
@@ -4,7 +4,8 @@
             [clojure.set :as set]
             [meta-merge.core :as mm]
             [reitit.trie :as trie]
-            [reitit.exception :as exception])
+            [reitit.exception :as exception]
+            [reitit.exception :as ex])
   #?(:clj
      (:import (java.util.regex Pattern)
               (java.util HashMap Map)
@@ -58,12 +59,15 @@
     (walk-one path (mapv identity data) raw-routes)))
 
 (defn map-data [f routes]
-  (mapv #(update % 1 f) routes))
+  (mapv (fn [[p ds]] [p (f p ds)]) routes))
 
-(defn merge-data [x]
+(defn merge-data [p x]
   (reduce
     (fn [acc [k v]]
-      (mm/meta-merge acc {k v}))
+      (try
+        (mm/meta-merge acc {k v})
+        (catch #?(:clj Exception, :cljs js/Error) e
+          (ex/fail! ::merge-data {:path p, :left acc, :right {k v}, :exception e}))))
     {} x))
 
 (defn resolve-routes [raw-routes {:keys [coerce] :as opts}]
diff --git a/modules/reitit-dev/src/reitit/dev/pretty.cljc b/modules/reitit-dev/src/reitit/dev/pretty.cljc
index fa631723..dfec05e4 100644
--- a/modules/reitit-dev/src/reitit/dev/pretty.cljc
+++ b/modules/reitit-dev/src/reitit/dev/pretty.cljc
@@ -335,3 +335,27 @@
        problems))
    (color :white "https://cljdoc.org/d/metosin/reitit/CURRENT/doc/basics/route-data-validation")
    [:break]])
+
+(defmethod format-exception :reitit.impl/merge-data [_ _ {:keys [path left right exception]}]
+  [:group
+   (text "Error merging route-data:")
+   [:break] [:break]
+   [:group
+    [:span (color :grey "-- On route -----------------------")]
+    [:break]
+    [:break]
+    (text path)
+    [:break]
+    [:break]
+    [:span (color :grey "-- Exception ----------------------")]
+    [:break]
+    [:break]
+    (color :red (exception/get-message exception))
+    [:break]
+    [:break]
+    (edn left {:margin 3})
+    [:break]
+    (edn right {:margin 3})]
+   [:break]
+   (color :white "https://cljdoc.org/d/metosin/reitit/CURRENT/doc/basics/route-data")
+   [:break]])
diff --git a/test/cljc/reitit/exception_test.cljc b/test/cljc/reitit/exception_test.cljc
index 971bd63d..bde403a7 100644
--- a/test/cljc/reitit/exception_test.cljc
+++ b/test/cljc/reitit/exception_test.cljc
@@ -43,7 +43,11 @@
       ["/api/{ipa"]
 
       #"Invalid route data"
-      ["/api/ipa" {::roles #{:adminz}}])
+      ["/api/ipa" {::roles #{:adminz}}]
+
+      #"Error merging route-data"
+      ["/a" {:body {}}
+       ["/b" {:body [:FAIL]}]])
 
     exception/exception
     pretty/exception))