diff --git a/examples/heif_info.cc b/examples/heif_info.cc
index 57d9a68988..96097ef3a8 100644
--- a/examples/heif_info.cc
+++ b/examples/heif_info.cc
@@ -570,7 +570,7 @@ int main(int argc, char** argv)
             long unsigned int data_len = heif_region_get_inline_mask_data_len(regions[j]);
             std::vector<uint8_t> mask_data(data_len);
             heif_region_get_inline_mask_data(regions[j], &x, &y, &w, &h, mask_data.data());
-            printf("      inline mask [x=%i, y=%i, w=%u, h=%u, data len=%lu]\n", x, y, w, h, mask_data.size());
+            printf("      inline mask [x=%i, y=%i, w=%u, h=%u, data len=%zu]\n", x, y, w, h, mask_data.size());
           }
       }