diff --git a/cmds/dumpstate/dumpstate.h b/cmds/dumpstate/dumpstate.h
index 2be340b..d17a677 100644
--- a/cmds/dumpstate/dumpstate.h
+++ b/cmds/dumpstate/dumpstate.h
@@ -31,7 +31,9 @@
 /* prints the contents of a file */
 int dump_file(const char *title, const char *path);
 
-/* prints the contents of the fd */
+/* prints the contents of the fd
+ * fd must have been opened with the flag O_NONBLOCK.
+ */
 int dump_file_from_fd(const char *title, const char *path, int fd);
 
 /* forks a command and waits for it to finish -- terminate args with NULL */