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	2021-05-09 16:00:11.000000000 -0600
+++ src/sage/libs/lcalc/lcalc_Lfunction.pyx	2021-06-02 17:12:56.077802570 -0600
@@ -1,5 +1,5 @@
 # distutils: libraries = m NTL_LIBRARIES Lfunction
-# distutils: extra_compile_args = NTL_CFLAGS -O3 -ffast-math
+# distutils: extra_compile_args = NTL_CFLAGS -std=gnu++11 -ffast-math
 # distutils: include_dirs = NTL_INCDIR
 # distutils: library_dirs = NTL_LIBDIR
 # distutils: extra_link_args = NTL_LIBEXTRA