diff --git a/lib/cartodb/backends/template_maps.js b/lib/cartodb/backends/template_maps.js
index 4175eba1..4f100a4f 100644
--- a/lib/cartodb/backends/template_maps.js
+++ b/lib/cartodb/backends/template_maps.js
@@ -206,23 +206,28 @@ TemplateMaps.prototype.addTemplate = function(owner, template, callback) {
     }
 
     self._redisCmd('HLEN', [ userTemplatesKey ], (err, numberOfTemplates) => {
-        assert.ifError(err);
+        if (err) {
+            return callback(err);
+        }
+
         if ( limit && numberOfTemplates >= limit ) {
-            var limitReachedError = new Error("User '" + owner + "' reached limit on number of templates (" +
-                numberOfTemplates + "/" + limit + ")");
+            var limitReachedError = new Error(
+                `User '${owner}' reached limit on number of templates (${numberOfTemplates}/${limit})`
+            );
             limitReachedError.http_status = 409;
-            throw limitReachedError;
+            return callback(limitReachedError);
         }
         self._redisCmd('HSETNX', [ userTemplatesKey, templateName, JSON.stringify(template) ], (err, wasSet) => {
-            assert.ifError(err);
-            if ( ! wasSet ) {
-                throw new Error("Template '" + templateName + "' of user '" + owner + "' already exists");
+            if (err) {
+                return callback(err);
             }
 
-            if (!err) {
-                self.emit('add', owner, templateName, template);
+            if (!wasSet) {
+                const ownerExistsError = new Error(`Template '${templateName}' of user '${owner}' already exists`);
+                return callback(ownerExistsError);
             }
 
+            self.emit('add', owner, templateName, template);
             callback(err, templateName, template);
         });
     });