diff --git a/src/usage_text.h b/src/usage_text.h
index 7ae1af40..9f33aa67 100644
--- a/src/usage_text.h
+++ b/src/usage_text.h
@@ -960,4 +960,11 @@
     "                              when aria2 exits.")
 #define TEXT_DSCP                                                       \
   _(" --dscp=DSCP                  Set DSCP value in outgoing IP packets of\n" \
-    "                              BitTorrent traffic for QoS.")
+    "                              BitTorrent traffic for QoS. This parameter sets\n" \
+    "                              only DSCP bits in TOS field of IP packets,\n" \
+    "                              not the whole field. If you take values\n" \
+    "                              from /usr/include/netinet/ip.h divide them by 4\n" \
+    "                              (otherwise values would be incorrect, e.g. your CS1\n" \
+    "                              class would turn into CS4). If you are take commonly\n" \
+    "                              used values from RFC, network vendors' documentation,\n" \
+    "                              Wikipedia or any other source, use them as they are.")