Index: include/asterisk/select.h
===================================================================
--- include/asterisk/select.h	(revision 313097)
+++ include/asterisk/select.h	(working copy)
@@ -33,6 +33,16 @@
 extern "C" {
 #endif
 
+/*!\note
+ * Number of file descriptors supported.  This needs to reduce the field size
+ * to the actual field size that we support.  Otherwise, we could end up with
+ * some select(2) call weirdness (either calls that error out immediately,
+ * because the size is too high, or calls that don't actually monitor anything,
+ * because the bits are higher than the maximum that the system will monitor).
+ *
+ * Initially defined in main/poll.c, though it may be modified in
+ * main/asterisk.c (main() function).
+ */
 extern unsigned int ast_FD_SETSIZE;
 
 #if !defined(HAVE_VARIABLE_FDSET) && defined(CONFIGURE_RAN_AS_ROOT)
@@ -56,10 +66,12 @@
 #define FD_SET(fd, fds) \
 	do { \
 		TYPEOF_FD_SET_FDS_BITS *bytes = (TYPEOF_FD_SET_FDS_BITS *) fds; \
-		if (fd / sizeof(*bytes) + ((fd + 1) % sizeof(*bytes) ? 1 : 0) < sizeof(*(fds))) { \
+		if (fd >= ast_FD_SETSIZE) { \
+			fprintf(stderr, "FD %d exceeds the maximum file descriptor permitted by this process (%d)\n", fd, ast_FD_SETSIZE); \
+		} else if (fd / sizeof(*bytes) + ((fd + 1) % sizeof(*bytes) ? 1 : 0) < sizeof(*(fds))) { \
 			bytes[fd / (sizeof(*bytes) * 8)] |= ((TYPEOF_FD_SET_FDS_BITS) 1) << (fd % (sizeof(*bytes) * 8)); \
 		} else { \
-			fprintf(stderr, "FD %d exceeds the maximum size of ast_fdset!\n", fd); \
+			fprintf(stderr, "FD %d exceeds the maximum size of ast_fdset! (increase ast_FDMAX in include/asterisk/select.h and recompile)\n", fd); \
 		} \
 	} while (0)
 #endif /* HAVE_VARIABLE_FDSET */
Index: main/asterisk.c
===================================================================
--- main/asterisk.c	(revision 313097)
+++ main/asterisk.c	(working copy)
@@ -3362,12 +3362,14 @@
 			break; /* XXX Should we exit() here? XXX */
 		}
 
-		fd2 = (l.rlim_cur > sizeof(readers) * 8 ? sizeof(readers) * 8 : l.rlim_cur) - 1;
+		fd2 = (l.rlim_cur >= sizeof(readers) * 8 ? sizeof(readers) * 8 : l.rlim_cur) - 1;
 		if (dup2(fd, fd2) < 0) {
 			ast_log(LOG_WARNING, "Cannot open maximum file descriptor %d at boot? %s\n", fd2, strerror(errno));
 			close(fd);
 			break;
 		}
+		/* Set here, because we reference the value in the FD_SET macro */
+		ast_FD_SETSIZE = fd2 + 1;
 
 		FD_ZERO(&readers);
 		FD_SET(fd2, &readers);