diff --git a/libsigrok-internal.h b/libsigrok-internal.h
index 0dfbbe8a..e63ea930 100644
--- a/libsigrok-internal.h
+++ b/libsigrok-internal.h
@@ -122,7 +122,7 @@ SR_PRIV int sr_source_add(int fd, int events, int timeout,
 /*--- session.c -------------------------------------------------------------*/
 
 SR_PRIV int sr_session_send(const struct sr_dev_inst *sdi,
-			    struct sr_datafeed_packet *packet);
+			    const struct sr_datafeed_packet *packet);
 
 /*--- hardware/common/serial.c ----------------------------------------------*/
 
diff --git a/libsigrok.h b/libsigrok.h
index 9946691e..f371c944 100644
--- a/libsigrok.h
+++ b/libsigrok.h
@@ -268,7 +268,7 @@ struct sr_context;
 
 struct sr_datafeed_packet {
 	uint16_t type;
-	void *payload;
+	const void *payload;
 };
 
 struct sr_datafeed_header {
@@ -336,7 +336,7 @@ struct sr_output_format {
 	int (*event) (struct sr_output *o, int event_type, uint8_t **data_out,
 		      uint64_t *length_out);
 	GString *(*recv) (struct sr_output *o, const struct sr_dev_inst *sdi,
-			struct sr_datafeed_packet *packet);
+			const struct sr_datafeed_packet *packet);
 	int (*cleanup) (struct sr_output *o);
 };
 
diff --git a/output/analog.c b/output/analog.c
index 448b112e..d2f28b6b 100644
--- a/output/analog.c
+++ b/output/analog.c
@@ -189,11 +189,11 @@ static void fancyprint(int unit, int mqflags, float value, GString *out)
 }
 
 static GString *receive(struct sr_output *o, const struct sr_dev_inst *sdi,
-		struct sr_datafeed_packet *packet)
+		const struct sr_datafeed_packet *packet)
 {
-	struct sr_datafeed_analog *analog;
+	const struct sr_datafeed_analog *analog;
 	struct context *ctx;
-	float *fdata;
+	const float *fdata;
 	int i, j;
 
 	(void)sdi;
@@ -214,7 +214,7 @@ static GString *receive(struct sr_output *o, const struct sr_dev_inst *sdi,
 		break;
 	case SR_DF_ANALOG:
 		analog = packet->payload;
-		fdata = (float *)analog->data;
+		fdata = (const float *)analog->data;
 		for (i = 0; i < analog->num_samples; i++) {
 			for (j = 0; j < ctx->num_enabled_probes; j++) {
 				g_string_append_printf(ctx->out, "%s: ",
diff --git a/proto.h b/proto.h
index c93a796e..870dc985 100644
--- a/proto.h
+++ b/proto.h
@@ -89,7 +89,7 @@ SR_API const struct sr_hwcap_option *sr_devopt_name_get(const char *optname);
 /*--- session.c -------------------------------------------------------------*/
 
 typedef void (*sr_datafeed_callback_t)(const struct sr_dev_inst *sdi,
-		struct sr_datafeed_packet *packet);
+		const struct sr_datafeed_packet *packet);
 
 /* Session setup */
 SR_API int sr_session_load(const char *filename);
diff --git a/session.c b/session.c
index 81e09b11..6a4a3c99 100644
--- a/session.c
+++ b/session.c
@@ -370,10 +370,10 @@ SR_API int sr_session_stop(void)
  *
  * @param packet The packet to show debugging information for.
  */
-static void datafeed_dump(struct sr_datafeed_packet *packet)
+static void datafeed_dump(const struct sr_datafeed_packet *packet)
 {
-	struct sr_datafeed_logic *logic;
-	struct sr_datafeed_analog *analog;
+	const struct sr_datafeed_logic *logic;
+	const struct sr_datafeed_analog *analog;
 
 	switch (packet->type) {
 	case SR_DF_HEADER:
@@ -426,7 +426,7 @@ static void datafeed_dump(struct sr_datafeed_packet *packet)
  * @private
  */
 SR_PRIV int sr_session_send(const struct sr_dev_inst *sdi,
-			    struct sr_datafeed_packet *packet)
+			    const struct sr_datafeed_packet *packet)
 {
 	GSList *l;
 	sr_datafeed_callback_t cb;