--- src/apprentice.c
+++ src/apprentice.c	2013-09-30 00:00:00.000000000 +0000
@@ -2072,8 +2072,16 @@ check_format_type(const char *ptr, int t
 		quad = 1;
 		/*FALLTHROUGH*/
 	case FILE_FMT_NUM:
+		if (*ptr == '#')
+			ptr++;
+		if (*ptr == ' ')
+			ptr++;
 		if (*ptr == '-')
 			ptr++;
+		if (*ptr == '+')
+			ptr++;
+		if (*ptr == '\'')
+			ptr++;
 		if (*ptr == '.')
 			ptr++;
 		while (isdigit((unsigned char)*ptr)) ptr++;
@@ -2115,6 +2123,9 @@ check_format_type(const char *ptr, int t
 				default:
 					return -1;
 				}
+			case 'o':
+			case 'x':
+			case 'X':
 			case 'd':
 				return 0;
 			default: