diff --git a/src/tool_cb_see.h b/src/tool_cb_see.h
index 530bfacba..1c14a8f74 100644
--- a/src/tool_cb_see.h
+++ b/src/tool_cb_see.h
@@ -27,6 +27,7 @@
 
 int tool_ftruncate64(int fd, curl_off_t where);
 
+#undef  ftruncate
 #define ftruncate(fd,where) tool_ftruncate64(fd,where)
 
 #ifndef HAVE_FTRUNCATE