diff --git a/libfprint/drivers/validity/validity_capture.c b/libfprint/drivers/validity/validity_capture.c
index c87630c1..8f808156 100644
--- a/libfprint/drivers/validity/validity_capture.c
+++ b/libfprint/drivers/validity/validity_capture.c
@@ -1085,7 +1085,7 @@ validity_capture_build_cmd_02 (const ValidityCaptureState   *capture,
 
   /* Debug: log chunk types and sizes */
   for (gsize i = 0; i < n_patched; i++)
-    fp_dbg ("cmd_02 chunk[%zu]: type=0x%02x size=%zu",
+    fp_dbg ("cmd_02 chunk[%zu]: type=0x%02x size=%u",
             i, patched[i].type, patched[i].size);
 
   /* Merge chunks back to binary */