diff --git a/vm.md b/vm.md
index 958f252..cefe248 100644
--- a/vm.md
+++ b/vm.md
@@ -54,6 +54,9 @@ Arithmetic instructions store their result in the last register specified.
 * Div
     * **Params**: REG1, REG2
     * `REG2 = REG1 / REG2`
+* Mod
+    * **Params**: REG1, REG2
+    * `REG2 = REG1 % REG2` (exact semantics TBD)
 * Neg
     * **Params**: REG1
     * `REG1 = REG1 * -1`