diff --git a/app/models/map.rb b/app/models/map.rb
index dd5e5604..cad2c360 100644
--- a/app/models/map.rb
+++ b/app/models/map.rb
@@ -86,10 +86,14 @@ class Map < ApplicationRecord
     user&.stars&.where(map: self)&.exists? || false # return false, not nil
   end
 
+  def fork_children_ids
+    Map.where(source_id: id).map(&:id)
+  end
+
   def as_json(_options = {})
     json = super(
       methods: [:user_name, :user_image, :star_count, :topic_count, :synapse_count,
-                :contributor_count, :collaborator_ids, :screenshot_url],
+                :contributor_count, :collaborator_ids, :screenshot_url, :fork_children_ids],
       except: [:screenshot_content_type, :screenshot_file_size, :screenshot_file_name,
                :screenshot_updated_at]
     )
diff --git a/frontend/src/Metamaps/Map/InfoBox.js b/frontend/src/Metamaps/Map/InfoBox.js
index 3f6fcd9c..f1714a41 100644
--- a/frontend/src/Metamaps/Map/InfoBox.js
+++ b/frontend/src/Metamaps/Map/InfoBox.js
@@ -362,26 +362,36 @@ const InfoBox = {
     event.stopPropagation()
   },
   deleteActiveMap: function() {
-    var confirmString = 'Are you sure you want to delete this map? '
+    let confirmString = 'Are you sure you want to delete this map? '
     confirmString += 'This action is irreversible. It will not delete the topics and synapses on the map.'
 
-    var doIt = window.confirm(confirmString)
-    var map = Active.Map
-    var mapper = Active.Mapper
-    var authorized = map.authorizePermissionChange(mapper)
+    const doIt = window.confirm(confirmString)
+    const map = Active.Map
+    const authorized = map.authorizePermissionChange(Active.Mapper)
 
-    if (doIt && authorized) {
-      InfoBox.close()
-      DataModel.Maps.Active.remove(map)
-      DataModel.Maps.Featured.remove(map)
-      DataModel.Maps.Mine.remove(map)
-      DataModel.Maps.Shared.remove(map)
-      map.destroy()
-      browserHistory.push('/')
-      GlobalUI.notifyUser('Map eliminated')
-    } else if (!authorized) {
-      window.alert("Hey now. We can't just go around willy nilly deleting other people's maps now can we? Run off and find something constructive to do, eh?")
+    if (!doIt) {
+      return
     }
+    if (!authorized) {
+      window.alert("Hey now. We can't just go around willy nilly deleting other people's maps now can we? Run off and find something constructive to do, eh?")
+      return
+    }
+    if (map.fork_children_ids.length > 0) {
+      let forkMessage = "This map has been forked, so it can't be deleted. The forked map idss are:"
+      forkMessage += map.fork_children_ids.join(', ')
+      window.alert(forkMessage)
+      return
+    }
+
+    // confirmed deletion, authorized, and no fork children
+    InfoBox.close()
+    DataModel.Maps.Active.remove(map)
+    DataModel.Maps.Featured.remove(map)
+    DataModel.Maps.Mine.remove(map)
+    DataModel.Maps.Shared.remove(map)
+    map.destroy()
+    browserHistory.push('/')
+    GlobalUI.notifyUser('Map eliminated')
   }
 }