diff --git a/src/lib/istream-private.h b/src/lib/istream-private.h
index c6b69d5754..ff6003a987 100644
--- a/src/lib/istream-private.h
+++ b/src/lib/istream-private.h
@@ -72,6 +72,7 @@ ssize_t i_stream_read_copy_from_parent(struct istream *istream);
 void i_stream_default_seek_nonseekable(struct istream_private *stream,
 				       uoff_t v_offset, bool mark);
 
+struct istream *i_stream_get_root_io(struct istream *stream);
 void i_stream_set_io(struct istream *stream, struct io *io);
 void i_stream_unset_io(struct istream *stream, struct io *io);
 
diff --git a/src/lib/istream.c b/src/lib/istream.c
index ab957a3000..3937118e17 100644
--- a/src/lib/istream.c
+++ b/src/lib/istream.c
@@ -682,15 +682,21 @@ bool i_stream_add_data(struct istream *_stream, const unsigned char *data,
 	return TRUE;
 }
 
-void i_stream_set_input_pending(struct istream *stream, bool pending)
+struct istream *i_stream_get_root_io(struct istream *stream)
 {
-	if (!pending)
-		return;
-
 	while (stream->real_stream->parent != NULL) {
 		i_assert(stream->real_stream->io == NULL);
 		stream = stream->real_stream->parent;
 	}
+	return stream;
+}
+
+void i_stream_set_input_pending(struct istream *stream, bool pending)
+{
+	if (!pending)
+		return;
+
+	stream = i_stream_get_root_io(stream);
 	if (stream->real_stream->io != NULL)
 		io_set_pending(stream->real_stream->io);
 }
@@ -706,10 +712,7 @@ void i_stream_switch_ioloop(struct istream *stream)
 
 void i_stream_set_io(struct istream *stream, struct io *io)
 {
-	while (stream->real_stream->parent != NULL) {
-		i_assert(stream->real_stream->io == NULL);
-		stream = stream->real_stream->parent;
-	}
+	stream = i_stream_get_root_io(stream);
 
 	i_assert(stream->real_stream->io == NULL);
 	stream->real_stream->io = io;
@@ -717,10 +720,7 @@ void i_stream_set_io(struct istream *stream, struct io *io)
 
 void i_stream_unset_io(struct istream *stream, struct io *io)
 {
-	while (stream->real_stream->parent != NULL) {
-		i_assert(stream->real_stream->io == NULL);
-		stream = stream->real_stream->parent;
-	}
+	stream = i_stream_get_root_io(stream);
 
 	i_assert(stream->real_stream->io == io);
 	stream->real_stream->io = NULL;