diff --git a/doc/optimization.txt b/doc/optimization.txt
index 974e2f9af2..3ed29fe38c 100644
--- a/doc/optimization.txt
+++ b/doc/optimization.txt
@@ -267,6 +267,11 @@ CELL/SPU:
 http://www-01.ibm.com/chips/techlib/techlib.nsf/techdocs/30B3520C93F437AB87257060006FFE5E/$file/Language_Extensions_for_CBEA_2.4.pdf
 http://www-01.ibm.com/chips/techlib/techlib.nsf/techdocs/9F820A5FFA3ECE8C8725716A0062585F/$file/CBE_Handbook_v1.1_24APR2007_pub.pdf
 
+RISC-V-specific:
+----------------
+The RISC-V Instruction Set Manual, Volume 1, Unprivileged ISA:
+https://riscv.org/technical/specifications/
+
 GCC asm links:
 --------------
 official doc but quite ugly