diff --git a/src/tool_cb_see.h b/src/tool_cb_see.h
index 530bfacbab77d9573e27079bffbc83c0161bc445..1c14a8f740802bc6d3136d642c4e7583e92fc567 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