diff --git a/src/runtime/c/configure.ac b/src/runtime/c/configure.ac
index 1a8f72b46..be8799b2f 100644
--- a/src/runtime/c/configure.ac
+++ b/src/runtime/c/configure.ac
@@ -34,10 +34,6 @@ AM_PROG_CC_C_O
  -Wno-unused-value"
 fi]
 
-
-AC_C_ALIGNOF
-AC_C_FAM_IN_MEM
-
 case "$target_cpu" in
 	i?86)	 cpu=i386; AC_DEFINE(LIGHTNING_I386, 1,
 		   [Define if lightning is targeting the x86 architecture]) ;;
diff --git a/src/runtime/c/gu/defs.h b/src/runtime/c/gu/defs.h
index 9fa62b39b..51a2293e3 100644
--- a/src/runtime/c/gu/defs.h
+++ b/src/runtime/c/gu/defs.h
@@ -56,13 +56,9 @@
 
 #ifdef GU_ALIGNOF
 # define gu_alignof GU_ALIGNOF
-# define GU_ALIGNOF_WORKS_ON_FAM_STRUCTS
 #else
 # define gu_alignof(t_) \
 	((size_t)(offsetof(struct { char c_; t_ e_; }, e_)))
-# ifdef GU_CAN_HAVE_FAM_IN_MEMBER
-#  define GU_ALIGNOF_WORKS_ON_FAM_STRUCTS
-# endif
 #endif
 
 #define GU_PLIT(type, expr) \
@@ -116,7 +112,7 @@ gu_min(int a, int b) {
 	return GU_MIN(a, b);
 }
 
-#ifdef GU_ALIGNOF_WORKS_ON_FAM_STRUCTS
+#ifdef GU_ALIGNOF
 #define gu_flex_alignof gu_alignof
 #else
 #define gu_flex_alignof(t) 0
diff --git a/src/runtime/c/m4/c_ext.m4 b/src/runtime/c/m4/c_ext.m4
deleted file mode 100644
index 8980a8407..000000000
--- a/src/runtime/c/m4/c_ext.m4
+++ /dev/null
@@ -1,42 +0,0 @@
-# AC_C_ALIGNOF
-# ------------
-# Check whether the C compiler supports the alignof(type) operator
-AC_DEFUN([AC_C_ALIGNOF],
-[
-  AC_CACHE_CHECK([for alignof],ac_cv_c_alignof,
-    [ac_cv_c_alignof=no
-     for ac_kw in alignof __alignof __alignof__; do
-       AC_COMPILE_IFELSE(
-	 [AC_LANG_PROGRAM([], [int align = $ac_kw (int);])],
-	 [ac_cv_c_alignof=$ac_kw; break])
-     done])
-  if test $ac_cv_c_alignof != no; then
-    AC_DEFINE([HAVE_ALIGNOF], 1,
-      [Define to 1 if alignof works on your compiler])
-    if test $ac_cv_c_alignof != alignof; then
-      AC_DEFINE_UNQUOTED([alignof], [$ac_cv_c_alignof],
-	[Define to the name of the alignof operator.])
-    fi
-  fi
-])
-
-# AC_C_FAM_IN_MEM
-# ---------------
-# Check whether the C compiler supports a flexible array member
-# in a struct that is the (last) member of a struct
-AC_DEFUN([AC_C_FAM_IN_MEM],
-[
-  AC_CACHE_CHECK([for flexible array members in struct members],
-    ac_cv_c_fam_in_mem,
-    [AC_COMPILE_IFELSE(
-      [AC_LANG_PROGRAM([
-	struct { struct { char foo[]; } bar; } baz;
-      ])], 
-      [ac_cv_c_fam_in_mem=yes],
-      [ac_cv_c_fam_in_mem=no])])
-  if test $ac_cv_c_fam_in_mem = yes; then
-    AC_DEFINE([CAN_HAVE_FAM_IN_MEMBER], 1,
-    [Define to 1 if a struct with flexible array members can be 
-     the last member of another struct.])
-  fi
-])