diff --git a/CHANGELOG.md b/CHANGELOG.md
index b165345c..735574e5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ## Last Changes
 
+- [#65](https://github.com/LaxarJS/laxar/issues/65): fixed navigation being broken when parameter values were missing.
 - [#66](https://github.com/LaxarJS/laxar/issues/66): prevented endless navigation ping pong in flow controller
 
 
diff --git a/lib/portal/modules/flow.js b/lib/portal/modules/flow.js
index fb2530ac..3c3e2cff 100644
--- a/lib/portal/modules/flow.js
+++ b/lib/portal/modules/flow.js
@@ -254,12 +254,7 @@ define( [
       var placeParameters = {};
       var params = place.fixedParameters || $routeParams;
       object.forEach( place.expectedParameters, function( parameterName ) {
-         if( typeof params[ parameterName ] === 'undefined' ) {
-            placeParameters[ parameterName ] = null;
-         }
-         else {
-            placeParameters[ parameterName ] = decodePlaceParameter( params[ parameterName ] );
-         }
+         placeParameters[ parameterName ] = decodePlaceParameter( params[ parameterName ] );
       } );
 
       return placeParameters;
@@ -272,10 +267,7 @@ define( [
       var location = '/' + placeName;
 
       object.forEach( place.expectedParameters, function( parameterName ) {
-         location += '/';
-         if( parameterName in parameters && parameters[ parameterName ] !== null ) {
-            location += encodePlaceParameter( parameters[ parameterName ] );
-         }
+         location += '/' + encodePlaceParameter( parameters[ parameterName ] );
       } );
 
       return location;
@@ -346,10 +338,10 @@ define( [
       if( placeName ) {
          var targetPlace = places_[ placeName ];
          var uri = placeName;
+         var parameters = entryPoint.parameters || {};
 
          object.forEach( targetPlace.expectedParameters, function( parameterName ) {
-            var param = entryPoint.parameters[ parameterName ] || '';
-            uri += '/' + encodePlaceParameter( param );
+            uri += '/' + encodePlaceParameter( parameters[ parameterName ] );
          } );
 
          return uri;
@@ -421,12 +413,18 @@ define( [
    ///////////////////////////////////////////////////////////////////////////////////////////////////////////
 
    function encodePlaceParameter( value ) {
+      if( value == null ) {
+         return '_';
+      }
       return typeof value === 'string' ? value.replace( /\//g, '%2F' ) : value;
    }
 
    ///////////////////////////////////////////////////////////////////////////////////////////////////////////
 
    function decodePlaceParameter( value ) {
+      if( value == null || value === '' || value === '_' ) {
+         return null;
+      }
       return typeof value === 'string' ? value.replace( /%2F/g, '/' ) : value;
    }
 
diff --git a/lib/portal/modules/spec/flow_spec.js b/lib/portal/modules/spec/flow_spec.js
index f6a7686f..bd435e37 100644
--- a/lib/portal/modules/spec/flow_spec.js
+++ b/lib/portal/modules/spec/flow_spec.js
@@ -404,6 +404,43 @@ define( [
 
                ///////////////////////////////////////////////////////////////////////////////////////////////
 
+               it( 'encodes null parameters as underscore (#65)', function() {
+                  eventBus.publish( 'navigateRequest.previous', {
+                     target: 'previous',
+                     data: {
+                        taskId: null
+                     }
+                  } );
+                  jasmine.Clock.tick( 0 );
+
+                  expect( $location.path ).toHaveBeenCalledWith( '/stepOne/_' );
+               } );
+
+               ///////////////////////////////////////////////////////////////////////////////////////////////
+
+               it( 'decodes underscores as null (#65)', function() {
+                  eventBus.publish.reset();
+                  $controller( 'portal.FlowController', {
+                     EventBus: eventBus,
+                     place: $route.routes[ '/stepOne' ].resolve.place(),
+                     // for everything apart from / we can rely on angular js to do the encoding
+                     $routeParams: { taskId: '_' },
+                     ThemeManager: {
+                        getTheme: function() { return 'myTheme'; }
+                     }
+                  } );
+                  jasmine.Clock.tick( 0 );
+
+                  expect( eventBus.publish )
+                     .toHaveBeenCalledWith( 'didNavigate.previous', {
+                        target: 'previous',
+                        place: 'stepOne/:taskId',
+                        data: { taskId: null }
+                     }, { sender: 'FlowController' } );
+               } );
+
+               ///////////////////////////////////////////////////////////////////////////////////////////////
+
                describe( 'to the currently active place again', function() {
 
                   beforeEach( function() {