diff --git a/spice/vd_agent.h b/spice/vd_agent.h
index 4e6fcf7..f24479d 100644
--- a/spice/vd_agent.h
+++ b/spice/vd_agent.h
@@ -45,6 +45,8 @@ typedef struct SPICE_ATTR_PACKED VDAgentMessage {
 
 #define VD_AGENT_PROTOCOL 1
 #define VD_AGENT_MAX_DATA_SIZE 2048
+#define VD_AGENT_CLIPBOARD_MAX_SIZE_DEFAULT 1024
+#define VD_AGENT_CLIPBOARD_MAX_SIZE_ENV "SPICE_CLIPBOARD_MAX_SIZE"
 
 enum {
     VD_AGENT_MOUSE_STATE = 1,