diff --git a/gui/app.js b/gui/app.js
index ba046244..8029f30b 100644
--- a/gui/app.js
+++ b/gui/app.js
@@ -648,6 +648,12 @@ syncthing.filter('shortPath', function () {
     }
 });
 
+syncthing.filter('clean', function () {
+    return function (input) {
+        return encodeURIComponent(input).replace(/%/g, '');
+    }
+});
+
 syncthing.directive('optionEditor', function () {
     return {
         restrict: 'C',
@@ -680,3 +686,25 @@ syncthing.directive('uniqueRepo', function() {
         }
     };
 });
+
+syncthing.directive('validNodeid', function() {
+    return {
+        require: 'ngModel',
+        link: function(scope, elm, attrs, ctrl) {
+            ctrl.$parsers.unshift(function(viewValue) {
+                if (scope.editingExisting) {
+                    // we shouldn't validate
+                    ctrl.$setValidity('validNodeid', true);
+                } else {
+                    var cleaned = viewValue.replace(/ /g, '').replace(/-/g, '').toUpperCase().trim();
+                    if (cleaned.match(/^[A-Z2-7]{52}$/)) {
+                        ctrl.$setValidity('validNodeid', true);
+                    } else {
+                        ctrl.$setValidity('validNodeid', false);
+                    }
+                }
+                return viewValue;
+            });
+        }
+    };
+});
diff --git a/gui/index.html b/gui/index.html
index 057e1615..a75f6765 100644
--- a/gui/index.html
+++ b/gui/index.html
@@ -125,13 +125,13 @@
           <div class="panel panel-{{repoClass(repo.ID)}}" ng-repeat="repo in repoList()">
             <div class="panel-heading">
               <h3 class="panel-title">
-                <a data-toggle="collapse" data-parent="#repositories" href="#repo-{{repo.ID}}">
+                <a data-toggle="collapse" data-parent="#repositories" href="#repo-{{repo.ID | clean}}">
                   <span class="glyphicon glyphicon-hdd"></span> {{repo.Directory | shortPath}}
                   <span class="pull-right hidden-xs">{{repoStatus(repo.ID)}}</span>
                 </a>
               </h3>
             </div>
-            <div id="repo-{{repo.ID}}" class="panel-collapse collapse">
+            <div id="repo-{{repo.ID | clean}}" class="panel-collapse collapse">
               <div class="panel-body">
                 <div class="table-responsive">
                   <table class="table table-condensed table-striped">
@@ -195,10 +195,10 @@
           <div class="panel panel-default" ng-repeat="nodeCfg in [thisNode()]">
             <div class="panel-heading">
               <h3 class="panel-title">
-                <a data-toggle="collapse" data-parent="#nodes" href="#node-{{nodeCfg.NodeID}}"><span class="glyphicon glyphicon-home"></span> {{nodeName(nodeCfg)}}</a>
+                <a data-toggle="collapse" data-parent="#nodes" href="#node-{{nodeCfg.NodeID | clean}}"><span class="glyphicon glyphicon-home"></span> {{nodeName(nodeCfg)}}</a>
               </h3>
             </div>
-            <div id="node-{{nodeCfg.NodeID}}" class="panel-collapse collapse in">
+            <div id="node-{{nodeCfg.NodeID | clean}}" class="panel-collapse collapse in">
               <div class="panel-body">
                 <div class="table-responsive">
                   <table class="table table-condensed table-striped">
@@ -415,13 +415,14 @@
           <form role="form" name="nodeEditor">
             <div class="form-group" ng-class="{'has-error': nodeEditor.nodeID.$invalid && nodeEditor.nodeID.$dirty}">
               <label for="nodeID">Node ID</label>
-              <input ng-if="!editingExisting" name="nodeID" id="nodeID" class="form-control text-monospace" type="text" ng-model="currentNode.NodeID" required></input>
+              <input ng-if="!editingExisting" name="nodeID" id="nodeID" class="form-control text-monospace" type="text" ng-model="currentNode.NodeID" required valid-nodeid></input>
               <div ng-if="editingExisting" class="well well-sm text-monospace">{{currentNode.NodeID | chunkID}}</div>
               <p class="help-block">
                 <span ng-if="nodeEditor.nodeID.$valid || nodeEditor.nodeID.$pristine">The node ID to enter here can be found in the "Edit > Show ID" dialog on the other node. Spaces and dashes are optional (ignored).
                   <span ng-show="!editingExisting">When adding a new node, keep in mind that <em>this node</em> must be added on the other side too.</span>
                 </span>
                 <span ng-if="nodeEditor.nodeID.$error.required && nodeEditor.nodeID.$dirty">The node ID cannot be blank.</span>
+                <span ng-if="nodeEditor.nodeID.$error.validNodeid && nodeEditor.nodeID.$dirty">The entered node ID does not look valid. It should be a 52 character string consisting of letters and numbers, with spaces and dashes being optional.</span>
               </p>
             </div>
             <div class="form-group">
@@ -460,11 +461,12 @@
               <div class="col-md-12">
                 <div class="form-group" ng-class="{'has-error': repoEditor.repoID.$invalid && repoEditor.repoID.$dirty}">
                   <label for="repoID">Repository ID</label>
-                  <input name="repoID" placeholder="documents" ng-disabled="editingExisting" id="repoID" class="form-control" type="text" ng-model="currentRepo.ID" required unique-repo></input>
+                  <input name="repoID" placeholder="documents" ng-disabled="editingExisting" id="repoID" class="form-control" type="text" ng-model="currentRepo.ID" required unique-repo ng-pattern="/^[a-zaZ0-9-_.]{1,64}$/"></input>
                   <p class="help-block">
                     <span ng-if="repoEditor.repoID.$valid || repoEditor.repoID.$pristine">Short identifier for the repository. Must be the same on all cluster nodes.</span>
                     <span ng-if="repoEditor.repoID.$error.uniqueRepo">The repository ID must be unique.</span>
                     <span ng-if="repoEditor.repoID.$error.required && repoEditor.repoID.$dirty">The repository ID cannot be blank.</span>
+                    <span ng-if="repoEditor.repoID.$error.pattern && repoEditor.repoID.$dirty">The repository ID must be a short identifier (64 characters or less) consisting of letters, numbers and the the <code>-_.</code> characters only.</span>
                   </p>
                 </div>
                 <div class="form-group" ng-class="{'has-error': repoEditor.repoPath.$invalid && repoEditor.repoPath.$dirty}">