diff --git a/libclamav/blob.h b/libclamav/blob.h
index 151609323..7d010b075 100644
--- a/libclamav/blob.h
+++ b/libclamav/blob.h
@@ -59,7 +59,7 @@ typedef	struct fileblob {
 	unsigned	int	isNotEmpty : 1;
 	unsigned	int	isInfected : 1;
 	unsigned	long	bytes_scanned;
-	cli_ctx	*ctx;
+	cli_ctx	*ctx;	/* When set we can scan the blob, otherwise NULL */
 } fileblob;
 
 fileblob	*fileblobCreate(void);
diff --git a/libclamav/message.h b/libclamav/message.h
index 6d49d493b..1ba08d61a 100644
--- a/libclamav/message.h
+++ b/libclamav/message.h
@@ -30,7 +30,7 @@ typedef struct message {
 	char	**mimeArguments;
 	char	*mimeDispositionType;	/* probably attachment */
 	text	*body_first, *body_last;
-	cli_ctx	*ctx;
+	cli_ctx	*ctx;	/* When set we can scan the message, otherwise NULL */
 
 	char	base64_1, base64_2, base64_3;
 	int	base64chars;