diff --git a/cores/esp32/Print.cpp b/cores/esp32/Print.cpp
index 8c295347..65fa1e9d 100644
--- a/cores/esp32/Print.cpp
+++ b/cores/esp32/Print.cpp
@@ -52,7 +52,7 @@ size_t Print::printf(const char *format, ...)
     va_list copy;
     va_start(arg, format);
     va_copy(copy, arg);
-    size_t len = vsnprintf(NULL, 0, format, arg);
+    size_t len = vsnprintf(NULL, 0, format, copy);
     va_end(copy);
     if(len >= sizeof(loc_buf)){
         temp = new char[len+1];