diff --git a/src/main/p4iodrv/device.c b/src/main/p4iodrv/device.c
index fc511c2..e13e326 100644
--- a/src/main/p4iodrv/device.c
+++ b/src/main/p4iodrv/device.c
@@ -39,8 +39,8 @@ static bool p4io_transfer(
     }
 
     if(resp_payload_len && transferred_response_payload != resp_payload_len) {
-        log_warning("Asked for %zu bytes got %zu", resp_payload_len,
-            transferred_response_payload);
+        log_warning("Asked for %u bytes got %u", (unsigned)resp_payload_len,
+            (unsigned)transferred_response_payload);
         return false;
     }
 
diff --git a/src/main/p4iodrv/usb.c b/src/main/p4iodrv/usb.c
index 858a212..ca4dfc4 100644
--- a/src/main/p4iodrv/usb.c
+++ b/src/main/p4iodrv/usb.c
@@ -137,7 +137,7 @@ bool p4io_usb_transfer(
 
     // must be 65 bytes or requests can stall - only 64 will ever be returned
     if(!ReadFile(bulk_handle, &cmd_buf, 65, &bytes_xferred, 0)) {
-        log_warning("ReadFile (%u) failed", bytes_requested);
+        log_warning("ReadFile (%u) failed", (unsigned)bytes_requested);
         return false;
     }