diff --git a/cores/esp32/esp32-hal-uart.c b/cores/esp32/esp32-hal-uart.c
index 157c3640830..0b507f833cf 100644
--- a/cores/esp32/esp32-hal-uart.c
+++ b/cores/esp32/esp32-hal-uart.c
@@ -481,11 +481,12 @@ int log_printf(const char *format, ...)
     va_list copy;
     va_start(arg, format);
     va_copy(copy, arg);
-    len = vsnprintf(NULL, 0, format, arg);
+    len = vsnprintf(NULL, 0, format, copy);
     va_end(copy);
     if(len >= sizeof(loc_buf)){
         temp = (char*)malloc(len+1);
         if(temp == NULL) {
+            va_end(arg);
             return 0;
         }
     }