diff --git a/libs/core/ksbit.h b/libs/core/ksbit.h
index 9f618477..f1d3f4b5 100644
--- a/libs/core/ksbit.h
+++ b/libs/core/ksbit.h
@@ -7,5 +7,6 @@ typedef ImageData* Image;
 typedef BufferData* Buffer;
 
 namespace pxt {
+  uint32_t programSize();
   uint32_t afterProgramPage();    
 }