diff --git a/lib/scp.h b/lib/scp.h
index 24239776..3275dc78 100644
--- a/lib/scp.h
+++ b/lib/scp.h
@@ -49,7 +49,7 @@
 
 #define SCP_AUTHKEY_ID_LEN 2
 
-#define SCP_MSG_BUF_SIZE 4096
+#define SCP_MSG_BUF_SIZE 3136
 
 // Message
 #pragma pack(push, 1)
diff --git a/lib/yubihsm.h b/lib/yubihsm.h
index 792e767a..30270234 100644
--- a/lib/yubihsm.h
+++ b/lib/yubihsm.h
@@ -88,7 +88,7 @@
 /// Length of host challenge for authentication
 #define YH_HOST_CHAL_LEN 8
 /// Maximum length of message buffer
-#define YH_MSG_BUF_SIZE 4096
+#define YH_MSG_BUF_SIZE 3136
 /// Length of authentication keys
 #define YH_KEY_LEN 16
 /// Device vendor ID