diff --git a/src/engine/sequencer.js b/src/engine/sequencer.js
index 5eca9c202..1498d6320 100644
--- a/src/engine/sequencer.js
+++ b/src/engine/sequencer.js
@@ -134,17 +134,10 @@ Sequencer.prototype.stepToReporter = function (thread, blockId, inputName) {
     currentStackFrame.waitingReporter = inputName;
     // Actually execute the block.
     this.startThread(thread);
-    if (thread.status === Thread.STATUS_YIELD ||
-        thread.status === Thread.STATUS_YIELD_BLOCK) {
-        // Reporter yielded; caller must wait for it to unyield.
-        // The value will be populated once the reporter unyields,
-        // and passed up to the currentStackFrame on next execution.
-        return true;
-    } else if (thread.status === Thread.STATUS_DONE) {
-        // Reporter finished, mark the thread as running.
-        thread.status = Thread.STATUS_RUNNING;
-        return false;
-    }
+    // If a reporter yielded, caller must wait for it to unyield.
+    // The value will be populated once the reporter unyields,
+    // and passed up to the currentStackFrame on next execution.
+    return thread.status === Thread.STATUS_YIELD;
 };
 
 /**
@@ -155,7 +148,8 @@ Sequencer.prototype.proceedThread = function (thread) {
     var currentBlockId = thread.peekStack();
     // Mark the status as done and proceed to the next block.
     this.runtime.glowBlock(currentBlockId, false);
-    thread.status = Thread.STATUS_DONE;
+    // If the block was yielding, move back to running state.
+    thread.status = Thread.STATUS_RUNNING;
     // Pop from the stack - finished this level of execution.
     thread.popStack();
     // Push next connected block, if there is one.
@@ -167,6 +161,10 @@ Sequencer.prototype.proceedThread = function (thread) {
     while (thread.peekStack() === null && thread.stack.length > 0) {
         thread.popStack();
     }
+    // If we still can't find a next block to run, mark the thread as done.
+    if (thread.peekStack() === null) {
+        thread.status = Thread.STATUS_DONE;
+    }
 };
 
 module.exports = Sequencer;
diff --git a/src/engine/thread.js b/src/engine/thread.js
index d14d83f90..e5c4df2e4 100644
--- a/src/engine/thread.js
+++ b/src/engine/thread.js
@@ -32,22 +32,23 @@ function Thread (firstBlock) {
 
 /**
  * Thread status for initialized or running thread.
- * Threads are in this state when the primitive is called for the first time.
+ * This is the default state for a thread - execution should run normally,
+ * stepping from block to block.
  * @const
  */
 Thread.STATUS_RUNNING = 0;
 
 /**
  * Thread status for a yielded thread.
- * Threads are in this state when a primitive has yielded.
+ * Threads are in this state when a primitive has yielded; execution is paused
+ * until the relevant primitive unyields.
  * @const
  */
 Thread.STATUS_YIELD = 1;
 
 /**
  * Thread status for a finished/done thread.
- * Thread is moved to this state when the interpreter
- * can proceed with execution.
+ * Thread is in this state when there are no more blocks to execute.
  * @const
  */
 Thread.STATUS_DONE = 2;