diff --git a/configure b/configure
index b5216ef185..60d545d5ff 100755
--- a/configure
+++ b/configure
@@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.ac Revision: 242889 .
+# From configure.ac Revision: 242974 .
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.61 for asterisk 1.6.
 #
@@ -18096,6 +18096,71 @@ fi
 rm -f core conftest.err conftest.$ac_objext conftest_ipa8_conftest.oo \
       conftest$ac_exeext conftest.$ac_ext
 
+# glibc, AFAIK, is the only C library that makes printing a NULL to a string safe.
+{ echo "$as_me:$LINENO: checking if your system printf is NULL-safe." >&5
+echo $ECHO_N "checking if your system printf is NULL-safe.... $ECHO_C" >&6; }
+if test "$cross_compiling" = yes; then
+  # It's unlikely an embedded system will have this.
+	{ echo "$as_me:$LINENO: result: unknown" >&5
+echo "${ECHO_T}unknown" >&6; }
+
+else
+  cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+#include <stdio.h>
+int
+main ()
+{
+printf("%s", NULL)
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest$ac_exeext
+if { (ac_try="$ac_link"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_link") 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && { ac_try='./conftest$ac_exeext'
+  { (case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_try") 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; }; then
+
+cat >>confdefs.h <<\_ACEOF
+#define HAVE_NULLSAFE_PRINTF 1
+_ACEOF
+
+	{ echo "$as_me:$LINENO: result: yes" >&5
+echo "${ECHO_T}yes" >&6; }
+else
+  echo "$as_me: program exited with status $ac_status" >&5
+echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+( exit $ac_status )
+{ echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+fi
+rm -f core *.core core.conftest.* gmon.out bb.out conftest$ac_exeext conftest.$ac_objext conftest.$ac_ext
+fi
+
+
+
 
 { echo "$as_me:$LINENO: checking for compiler 'attribute pure' support" >&5
 echo $ECHO_N "checking for compiler 'attribute pure' support... $ECHO_C" >&6; }
diff --git a/configure.ac b/configure.ac
index 6c86c985b5..d4a980dc18 100644
--- a/configure.ac
+++ b/configure.ac
@@ -589,6 +589,18 @@ AC_DEFINE([HAVE_GCC_ATOMICS], 1, [Define to 1 if your GCC C compiler provides at
 AC_MSG_RESULT(no)
 )
 
+# glibc, AFAIK, is the only C library that makes printing a NULL to a string safe.
+AC_MSG_CHECKING([if your system printf is NULL-safe.])
+AC_RUN_IFELSE(
+	AC_LANG_PROGRAM([#include <stdio.h>],
+		[printf("%s", NULL)]),
+	AC_DEFINE([HAVE_NULLSAFE_PRINTF], 1, [Define to 1 if your C library can safely print NULL to string formats.])
+	AC_MSG_RESULT(yes),
+	AC_MSG_RESULT(no),
+	# It's unlikely an embedded system will have this.
+	AC_MSG_RESULT(unknown)
+)
+
 AST_GCC_ATTRIBUTE(pure)
 AST_GCC_ATTRIBUTE(malloc)
 AST_GCC_ATTRIBUTE(const)
diff --git a/include/asterisk/autoconfig.h.in b/include/asterisk/autoconfig.h.in
index b8f3afaa82..46f8b2aa20 100644
--- a/include/asterisk/autoconfig.h.in
+++ b/include/asterisk/autoconfig.h.in
@@ -533,6 +533,9 @@
 /* Define to the version of the newt library. */
 #undef HAVE_NEWT_VERSION
 
+/* Define to 1 if your C library can safely print NULL to string formats. */
+#undef HAVE_NULLSAFE_PRINTF
+
 /* Define to 1 if your ODBC library has wide (Unicode) types. */
 #undef HAVE_ODBC_WCHAR
 
diff --git a/res/res_agi.c b/res/res_agi.c
index 4f03a4f58e..495602baa3 100644
--- a/res/res_agi.c
+++ b/res/res_agi.c
@@ -2546,7 +2546,7 @@ static char *help_workhorse(int fd, char *match[])
 		ast_join(fullcmd, sizeof(fullcmd), e->cmda);
 		if (match && strncasecmp(matchstr, fullcmd, strlen(matchstr)))
 			continue;
-		ast_cli(fd, "%5.5s %30.30s   %s\n", e->dead ? "Yes" : "No" , fullcmd, e->summary);
+		ast_cli(fd, "%5.5s %30.30s   %s\n", e->dead ? "Yes" : "No" , fullcmd, S_OR(e->summary, "Not available"));
 	}
 	AST_RWLIST_UNLOCK(&agi_commands);
 
@@ -2561,15 +2561,21 @@ int ast_agi_register(struct ast_module *mod, agi_command *cmd)
 
 	if (!find_command(cmd->cmda,1)) {
 		cmd->docsrc = AST_STATIC_DOC;
-#ifdef AST_XML_DOCS
 		if (ast_strlen_zero(cmd->summary) && ast_strlen_zero(cmd->usage)) {
-			cmd->summary = ast_xmldoc_build_synopsis("agi", fullcmd);
-			cmd->usage = ast_xmldoc_build_description("agi", fullcmd);
-			cmd->syntax = ast_xmldoc_build_syntax("agi", fullcmd);
-			cmd->seealso = ast_xmldoc_build_seealso("agi", fullcmd);
-			cmd->docsrc = AST_XML_DOC;
-		}
+#ifdef AST_XML_DOCS
+			*((char **) &cmd->summary) = ast_xmldoc_build_synopsis("agi", fullcmd);
+			*((char **) &cmd->usage) = ast_xmldoc_build_description("agi", fullcmd);
+			*((char **) &cmd->syntax) = ast_xmldoc_build_syntax("agi", fullcmd);
+			*((char **) &cmd->seealso) = ast_xmldoc_build_seealso("agi", fullcmd);
+			*((enum ast_doc_src *) &cmd->docsrc) = AST_XML_DOC;
+#elif (!defined(HAVE_NULLSAFE_PRINTF))
+			*((char **) &cmd->summary) = ast_strdup("");
+			*((char **) &cmd->usage) = ast_strdup("");
+			*((char **) &cmd->syntax) = ast_strdup("");
+			*((char **) &cmd->seealso) = ast_strdup("");
 #endif
+		}
+
 		cmd->mod = mod;
 		AST_RWLIST_WRLOCK(&agi_commands);
 		AST_LIST_INSERT_TAIL(&agi_commands, cmd, list);
@@ -2810,9 +2816,13 @@ static int agi_handle_command(struct ast_channel *chan, AGI *agi, char *buf, int
 				"Result: %s\r\n", chan->name, command_id, ami_cmd, resultcode, ami_res);
 		switch(res) {
 		case RESULT_SHOWUSAGE:
-			ast_agi_send(agi->fd, chan, "520-Invalid command syntax.  Proper usage follows:\n");
-			ast_agi_send(agi->fd, chan, "%s", c->usage);
-			ast_agi_send(agi->fd, chan, "520 End of proper usage.\n");
+			if (ast_strlen_zero(c->usage)) {
+				ast_agi_send(agi->fd, chan, "520 Invalid command syntax.  Proper usage not available.\n");
+			} else {
+				ast_agi_send(agi->fd, chan, "520-Invalid command syntax.  Proper usage follows:\n");
+				ast_agi_send(agi->fd, chan, "%s", c->usage);
+				ast_agi_send(agi->fd, chan, "520 End of proper usage.\n");
+			}
 			break;
 		case RESULT_FAILURE:
 			/* They've already given the failure.  We've been hung up on so handle this
@@ -2993,7 +3003,7 @@ static char *handle_cli_agi_show(struct ast_cli_entry *e, int cmd, struct ast_cl
 	case CLI_INIT:
 		e->command = "agi show commands [topic]";
 		e->usage =
-			"Usage: agi show commands [topic]\n"
+			"Usage: agi show commands [topic] <topic>\n"
 			"       When called with a topic as an argument, displays usage\n"
 			"       information on the given command.  If called without a\n"
 			"       topic, it provides a list of AGI commands.\n";