diff -up src/sage/libs/lcalc/lcalc_Lfunction.pyx.orig src/sage/libs/lcalc/lcalc_Lfunction.pyx
--- src/sage/libs/lcalc/lcalc_Lfunction.pyx.orig	2020-10-24 11:37:59.000000000 -0600
+++ src/sage/libs/lcalc/lcalc_Lfunction.pyx	2020-10-30 14:40:53.875121354 -0600
@@ -1,5 +1,5 @@
 # distutils: libraries = m ntl Lfunction
-# distutils: extra_compile_args = -O3 -ffast-math
+# distutils: extra_compile_args = -std=gnu++11 -ffast-math
 # distutils: language = c++
 r"""
 Rubinstein's lcalc library