diff --git a/src/client/Response.cxx b/src/client/Response.cxx
index 0c9145a50..b582d6bbc 100644
--- a/src/client/Response.cxx
+++ b/src/client/Response.cxx
@@ -61,7 +61,12 @@ Response::WriteBinary(ConstBuffer<void> payload) noexcept
 {
 	assert(payload.size <= client.binary_limit);
 
-	return Format("binary: %zu\n", payload.size) &&
+	return
+#ifdef _WIN32
+		Format("binary: %lu\n", (unsigned long)payload.size) &&
+#else
+		Format("binary: %zu\n", payload.size) &&
+#endif
 		Write(payload.data, payload.size) &&
 		Write("\n");
 }
diff --git a/src/command/FileCommands.cxx b/src/command/FileCommands.cxx
index 739cc6579..e5638a10a 100644
--- a/src/command/FileCommands.cxx
+++ b/src/command/FileCommands.cxx
@@ -231,7 +231,12 @@ read_stream_art(Response &r, const char *uri, size_t offset)
 		read_size = is->Read(lock, buffer.get(), buffer_size);
 	}
 
+#ifdef _WIN32
+	r.Format("size: %lu\n", (unsigned long)art_file_size);
+#else
 	r.Format("size: %" PRIoffset "\n", art_file_size);
+#endif
+
 	r.WriteBinary({buffer.get(), read_size});
 
 	return CommandResult::OK;
@@ -313,7 +318,11 @@ public:
 			return;
 		}
 
+#ifdef _WIN32
+		response.Format("size: %lu\n", (unsigned long)buffer.size);
+#else
 		response.Format("size: %zu\n", buffer.size);
+#endif
 
 		if (mime_type != nullptr)
 			response.Format("type: %s\n", mime_type);