diff --git a/src/engine/thread.js b/src/engine/thread.js
index 3b17ab6190..b0cb410b0f 100644
--- a/src/engine/thread.js
+++ b/src/engine/thread.js
@@ -451,7 +451,8 @@ class Thread {
         let callCount = 5; // Max number of enclosing procedure calls to examine.
         const sp = this.stackFrames.length - 1;
         for (let i = sp - 1; i >= 0; i--) {
-            const block = this.target.blocks.getBlock(this.stackFrames[i].op.id);
+            const block = this.target.blocks.getBlock(this.stackFrames[i].op.id) ||
+                this.target.runtime.flyoutBlocks.getBlock(this.stackFrames[i].op.id);
             if (block.opcode === 'procedures_call' &&
                 block.mutation.proccode === procedureCode) {
                 return true;