diff --git a/src/lib-mail/message-header-parser.c b/src/lib-mail/message-header-parser.c
index 3db3e4ab97..97d4205241 100644
--- a/src/lib-mail/message-header-parser.c
+++ b/src/lib-mail/message-header-parser.c
@@ -3,6 +3,7 @@
 #include "lib.h"
 #include "buffer.h"
 #include "istream.h"
+#include "istream-nonuls.h"
 #include "str.h"
 #include "message-size.h"
 #include "message-header-parser.h"
@@ -28,12 +29,16 @@ message_parse_header_init(struct istream *input, struct message_size *hdr_size,
 	struct message_header_parser_ctx *ctx;
 
 	ctx = i_new(struct message_header_parser_ctx, 1);
-	ctx->input = input;
+	if ((flags & MESSAGE_HEADER_REPLACE_NULS_WITH_0x80) != 0)
+		ctx->input = i_stream_create_nonuls(input, 0x80);
+	else {
+		ctx->input = input;
+		i_stream_ref(input);
+	}
 	ctx->hdr_size = hdr_size;
 	ctx->name = str_new(default_pool, 128);
 	ctx->flags = flags;
 	ctx->value_buf = buffer_create_dynamic(default_pool, 4096);
-	i_stream_ref(input);
 
 	if (hdr_size != NULL)
 		i_zero(hdr_size);
diff --git a/src/lib-mail/message-header-parser.h b/src/lib-mail/message-header-parser.h
index d6863524aa..38594bd18c 100644
--- a/src/lib-mail/message-header-parser.h
+++ b/src/lib-mail/message-header-parser.h
@@ -13,7 +13,9 @@ enum message_header_parser_flags {
 	/* Don't add CRs to full_value even if input had them */
 	MESSAGE_HEADER_PARSER_FLAG_DROP_CR		= 0x02,
 	/* Convert [CR+]LF+LWSP to a space character in full_value */
-	MESSAGE_HEADER_PARSER_FLAG_CLEAN_ONELINE	= 0x04
+	MESSAGE_HEADER_PARSER_FLAG_CLEAN_ONELINE	= 0x04,
+	/* Replace 0x0 symbols with 0x80 */
+	MESSAGE_HEADER_REPLACE_NULS_WITH_0x80		= 0x08,
 };
 
 struct message_header_line {