diff --git a/output/outieee.c b/output/outieee.c
index 7d723900..6c319cda 100644
--- a/output/outieee.c
+++ b/output/outieee.c
@@ -1120,7 +1120,7 @@ static void ieee_putascii(char *format, ...)
     va_list ap;
 
     va_start(ap, format);
-    vsprintf(buffer, format, ap);
+    vsnprintf(buffer, sizeof(buffer), format, ap);
     l = strlen(buffer);
     for (i = 0; i < l; i++)
         if ((buffer[i] & 0xff) > 31)