diff --git a/menelaus.scm b/menelaus.scm
index 19153b2..3415b3b 100644
--- a/menelaus.scm
+++ b/menelaus.scm
@@ -201,19 +201,18 @@
   (call-c-func "usb_init")
   (pause 200))
 
-(define (usb-send modifiers k0 k1 k2 k3 k4 k5)
+(define (usb-send m k0 k1 k2 k3 k4 k5)
   ;; call-c-func is a special form and cannot be applied
-  (call-c-func "usb_send"
-               (vector-ref modifiers 0) (vector-ref modifiers 1)
-               (vector-ref modifiers 2) (vector-ref modifiers 3)
-               k0 k1 k2 k3 k4 k5))
+  (let ((mods (+ (vector-ref m 0) (* (vector-ref m 1) 2)))) ; plus isn't variadic
+    (let ((mods (+ mods (+ (* (vector-ref m 2) 4) (* (vector-ref m 3) 8)))))
+      (call-c-func "usb_send" mods k0 k1 k2 k3 k4 k5))))
 
 (define (loop)
   ;; scanning the matrix tells us only which physical keys were pressed and
   ;; how many; it doesn't tell us which keycodes to send yet.
   (free! (let ((keys-scanned (debounce-matrix)))
            (set-usb-frame (press/release-for keys-scanned))
-           (apply usb-send modifiers (vector->list keycodes-down))))
+           (apply usb-send (cons modifiers (vector->list keycodes-down)))))
   (loop))
 
 (init)
diff --git a/test.rkt b/test.rkt
index c37525a..eb95943 100644
--- a/test.rkt
+++ b/test.rkt
@@ -18,12 +18,14 @@
 
 (define last-usb-frame #f) ; save this off so we can test it
 
-(define (usb-save ctrl shift alt supr . args)
-  (set! last-usb-frame (cons (filter symbol? (list (if (= 1 ctrl) 'ctrl 0)
-                                                   (if (= 1 shift) 'shift 0)
-                                                   (if (= 1 alt) 'alt 0)
-                                                   (if (= 1 supr) 'super 0)))
-                             args)))
+(define (mods-list mods)
+  (filter symbol? (list (if (positive? (bitwise-and mods 1)) 'ctrl 0)
+                        (if (positive? (bitwise-and mods 2)) 'shift 0)
+                        (if (positive? (bitwise-and mods 4)) 'alt 0)
+                        (if (positive? (bitwise-and mods 8)) 'super 0))))
+
+(define (usb-save mods . args)
+  (set! last-usb-frame (cons (mods-list mods) args)))
 
 (define (call-c-func f-name . args)
   (when (equal? f-name "usb_send")
diff --git a/usb_keyboard.c b/usb_keyboard.c
index f531d78..7625ebf 100644
--- a/usb_keyboard.c
+++ b/usb_keyboard.c
@@ -337,10 +337,10 @@ int8_t usb_keyboard_send(void)
 }
 
 // my own wrapper, mangled to work with the PoC microsheme FFI
-int16_t usb_send(int ctrl, int shift, int alt, int gui,
+int16_t usb_send(int modifiers,
                  int key0, int key1, int key2,
                  int key3, int key4, int key5) {
-  keyboard_modifier_keys = (uint8_t) (ctrl) | (shift<<1) | (alt<<2) | (gui<<3);
+  keyboard_modifier_keys = (uint8_t) modifiers;
   keyboard_keys[0] = (uint8_t)key0;
   keyboard_keys[1] = (uint8_t)key1;
   keyboard_keys[2] = (uint8_t)key2;