diff --git a/gpio.c b/gpio.c
--- a/gpio.c
+++ b/gpio.c
@@ -21,17 +21,19 @@ void user_input(uint16_t* to_modify)
 
 
 // Increment/decrement signed variable with up/down buttons
-void user_input_signed(int16_t* to_modify)
+void user_input_signed(int32_t* to_modify)
 {
-    // TODO: Bounds check on int16_t
+	//fixme: need to cast to 16/32 bits correctly
     if(CHANGE_ELAPSED) {
         if(!HAL_GPIO_ReadPin(SW_UP) ) {
             CHANGE_RESET;
-            (*to_modify)++;
+            if (*to_modify < 32768)
+            	(*to_modify)++;
         }
         else if(!HAL_GPIO_ReadPin(SW_DOWN)) {
             CHANGE_RESET;
-            (*to_modify)--;
+            if (*to_modify >= -32768)
+            	(*to_modify)--;
         }
     }
 }