diff --git a/sw/tools/gen_airframe.ml b/sw/tools/gen_airframe.ml
index 458f6073542..3ce7e5ad182 100644
--- a/sw/tools/gen_airframe.ml
+++ b/sw/tools/gen_airframe.ml
@@ -177,7 +177,7 @@ let parse_command_laws = fun command ->
        and rate_min = a "rate_min"
        and rate_max = a "rate_max" in
        let v = preprocess_value value "values" "COMMAND" in
-       printf "  static int16_t _var_%s = 0; _var_%s = Chop((%s) - (_var_%s), (%s), (%s));\\\n" var var v var rate_min rate_max
+       printf "  static int16_t _var_%s = 0; _var_%s += Chop((%s) - (_var_%s), (%s), (%s));\\\n" var var v var rate_min rate_max
    | "define" ->
        parse_element "" command
    | _ -> xml_error "set|let"