Index: funcs/func_strings.c
===================================================================
--- funcs/func_strings.c	(revision 137113)
+++ funcs/func_strings.c	(working copy)
@@ -300,8 +300,13 @@
 				formatbuf[&arg.format[i] - formatstart + 1] = '\0';
 
 				/* Convert the argument into the required type */
-				if (sscanf(arg.var[argcount++], "%d", &tmpi) != 1) {
-					ast_log(LOG_ERROR, "Argument '%s' is not an integer number for format '%s'\n", arg.var[argcount - 1], formatbuf);
+				if (arg.var[argcount]) {
+					if (sscanf(arg.var[argcount++], "%d", &tmpi) != 1) {
+						ast_log(LOG_ERROR, "Argument '%s' is not an integer number for format '%s'\n", arg.var[argcount - 1], formatbuf);
+						goto sprintf_fail;
+					}
+				} else {
+					ast_log(LOG_ERROR, "SPRINTF() has more format specifiers than arguments!\n");
 					goto sprintf_fail;
 				}
 
@@ -318,8 +323,13 @@
 				formatbuf[&arg.format[i] - formatstart + 1] = '\0';
 
 				/* Convert the argument into the required type */
-				if (sscanf(arg.var[argcount++], "%lf", &tmpd) != 1) {
-					ast_log(LOG_ERROR, "Argument '%s' is not a floating point number for format '%s'\n", arg.var[argcount - 1], formatbuf);
+				if (arg.var[argcount]) {
+					if (sscanf(arg.var[argcount++], "%lf", &tmpd) != 1) {
+						ast_log(LOG_ERROR, "Argument '%s' is not a floating point number for format '%s'\n", arg.var[argcount - 1], formatbuf);
+						goto sprintf_fail;
+					}
+				} else {
+					ast_log(LOG_ERROR, "SPRINTF() has more format specifiers than arguments!\n");
 					goto sprintf_fail;
 				}