--- a/am/ax_compile_check_rettype.m4
+++ b/am/ax_compile_check_rettype.m4
@@ -70,6 +70,7 @@ AC_CACHE_VAL(AC_CV_NAME,
 [for ac_type in char short int long "long long" $4
  do 
   AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+#include <sys/sysmacros.h>
 #include <sys/types.h>
 $3
 ]], [[switch (0) case 0: case (sizeof ($1($2)) == sizeof ($ac_type)):;]])], [AC_CV_NAME=$ac_type])