diff --git a/jspsych.js b/jspsych.js
index 188e8a0c..1cf2a093 100755
--- a/jspsych.js
+++ b/jspsych.js
@@ -489,8 +489,8 @@ window.jsPsych = (function() {
         // check for on_timeline_start and conditonal function on nodes with timelines
         if (typeof timeline_parameters != 'undefined') {
           // only run the conditional function if this is the first repetition of the timeline when
-          // repetitions > 1
-          if (typeof timeline_parameters.conditional_function !== 'undefined' && progress.current_repetition==0) {
+          // repetitions > 1, and only when on the first variable set
+          if (typeof timeline_parameters.conditional_function !== 'undefined' && progress.current_repetition==0 && progress.current_variable_set == 0) {
             var conditional_result = timeline_parameters.conditional_function();
             // if the conditional_function() returns false, then the timeline
             // doesn't run and is marked as complete.
diff --git a/tests/jsPsych/timelines.test.js b/tests/jsPsych/timelines.test.js
index ec5a8eca..d96a2a48 100644
--- a/tests/jsPsych/timelines.test.js
+++ b/tests/jsPsych/timelines.test.js
@@ -301,6 +301,41 @@ describe('conditional function', function(){
     expect(conditional_count).toBe(1);
   })
 
+  test('executes only once when timeline variables are used', function(){
+    var conditional_count = 0;
+
+    var trial = {
+      timeline: [{
+        type: 'html-keyboard-response',
+        stimulus: 'foo'
+      }],
+      timeline_variables: [
+        {a:1},
+        {a:2}
+      ],
+      conditional_function: function(){
+        conditional_count++;
+        return true;
+      }
+    }
+
+    jsPsych.init({
+      timeline: [trial]
+    });
+
+    expect(conditional_count).toBe(1);
+
+    // first trial
+    utils.pressKey(32);
+
+    expect(conditional_count).toBe(1);
+
+    // second trial
+    utils.pressKey(32);
+
+    expect(conditional_count).toBe(1);
+  })
+
   test('timeline variables from nested timelines are available', function(){
     var trial = {
       type: 'html-keyboard-response',