diff --git a/Makefile b/Makefile
index 8e8f461..a304627 100644
--- a/Makefile
+++ b/Makefile
@@ -3,6 +3,8 @@ RM=rm
 CC=cc
 ECHO=echo
 
+CFLAGS=-Wall
+
 OBJS=\
 $(OBJDIR)/p1load.o \
 $(OBJDIR)/ploader.o
diff --git a/p1load.c b/p1load.c
index 10b5ceb..643dd9b 100644
--- a/p1load.c
+++ b/p1load.c
@@ -44,9 +44,25 @@ enum {
     CHECK_PORT_NO_PROPELLER
 };
 
-static void cb_reset(void *data) { hwreset(); }
-static int cb_tx(void *data, uint8_t* buf, int n) { return tx(buf, n); }
-static int cb_rx_timeout(void *data, uint8_t* buf, int n, int timeout) { return rx_timeout(buf, n, timeout); }
+#define UNUSED(x)
+
+static void cb_reset(void *data)
+{
+    UNUSED(data); // osint keeps its state in globals
+    hwreset();
+}
+
+static int cb_tx(void *data, uint8_t* buf, int n)
+{
+    UNUSED(data); // osint keeps its state in globals
+    return tx(buf, n);
+}
+
+static int cb_rx_timeout(void *data, uint8_t* buf, int n, int timeout)
+{
+    UNUSED(data); // osint keeps its state in globals
+    return rx_timeout(buf, n, timeout);
+}
 
 static PL_serial serial = { cb_reset, cb_tx, cb_rx_timeout };
 static PL_state state;