--- a/configure.ac	Wed Nov 06 20:34:54 2019 +0100
+++ b/configure.ac	Wed Nov 06 21:01:25 2019 +0100
@@ -46,10 +46,7 @@
 LT_INIT
 
 # we want c11, and may fall back to c99
-AX_CHECK_COMPILE_FLAG([-std=c11],
-    [AX_APPEND_FLAG([-std=c11])],
-    AC_PROG_CC_C99
-)
+AC_PROG_CC_C99
 
 # we want to support automake < 1.14, so we need this deprecated macro
 # it tests, whether the compiler allows -c and -o simultaneously