diff --git a/m4/ax_append_to_file.m4 b/m4/ax_append_to_file.m4
index 15395178c..f9f54e088 100644
--- a/m4/ax_append_to_file.m4
+++ b/m4/ax_append_to_file.m4
@@ -23,5 +23,5 @@
 
 AC_DEFUN([AX_APPEND_TO_FILE],[
 AC_REQUIRE([AX_FILE_ESCAPES])
-printf -- "$2\n" >> "$1"
+printf "$2\n" >> "$1"
 ])
diff --git a/m4/ax_debug.m4 b/m4/ax_debug.m4
index 5ea3c3594..7696a1147 100644
--- a/m4/ax_debug.m4
+++ b/m4/ax_debug.m4
@@ -52,8 +52,8 @@ AC_DEFUN([AX_DEBUG],
         [Add debug code/turns off optimizations (yes|no) @<:@default=no@:>@])],
       [ax_enable_debug=yes
       AC_DEFINE([DEBUG],[1],[Define to 1 to enable debugging code.])
-      AX_ADD_AM_MACRO([--debug],[AM_YFLAGS])
-      AX_ADD_AM_MACRO([-D_GLIBCXX_DEBUG],[AM_CPPFLAGS])],
+      AX_ADD_AM_MACRO([AM_YFLAGS += --debug])
+      AX_ADD_AM_MACRO([AM_CPPFLAGS += -D_GLIBCXX_DEBUG])],
       [ax_enable_debug=no
       AC_SUBST([MCHECK])
       AC_DEFINE([DEBUG],[0],[Define to 1 to enable debugging code.])])