diff --git a/src/hardware/demo/api.c b/src/hardware/demo/api.c
index f23cb700..c5259b28 100644
--- a/src/hardware/demo/api.c
+++ b/src/hardware/demo/api.c
@@ -400,6 +400,7 @@ static int dev_acquisition_start(const struct sr_dev_inst *sdi)
 
 	devc = sdi->priv;
 	devc->sent_samples = 0;
+	devc->sent_frame_samples = 0;
 
 	/*
 	 * Determine the numbers of logic and analog channels that are
diff --git a/src/hardware/demo/protocol.c b/src/hardware/demo/protocol.c
index 37417f73..46808fd6 100644
--- a/src/hardware/demo/protocol.c
+++ b/src/hardware/demo/protocol.c
@@ -460,9 +460,6 @@ SR_PRIV int demo_prepare_data(int fd, int revents, void *cb_data)
 	samples_todo = (todo_us * devc->cur_samplerate + G_USEC_PER_SEC - 1)
 			/ G_USEC_PER_SEC;
 
-	if (SAMPLES_PER_FRAME > 0)
-		samples_todo = SAMPLES_PER_FRAME;
-
 	if (devc->limit_samples > 0) {
 		if (devc->limit_samples < devc->sent_samples)
 			samples_todo = 0;
@@ -470,6 +467,16 @@ SR_PRIV int demo_prepare_data(int fd, int revents, void *cb_data)
 			samples_todo = devc->limit_samples - devc->sent_samples;
 	}
 
+	if (samples_todo == 0)
+		return G_SOURCE_CONTINUE;
+
+#if (SAMPLES_PER_FRAME > 0) /* Avoid "comparison < 0 always false" warning. */
+	/* Never send more samples than a frame can fit... */
+	samples_todo = MIN(samples_todo, SAMPLES_PER_FRAME);
+	/* ...or than we need to finish the current frame. */
+	samples_todo = MIN(samples_todo, SAMPLES_PER_FRAME - devc->sent_frame_samples);
+#endif
+
 	/* Calculate the actual time covered by this run back from the sample
 	 * count, rounded towards zero. This avoids getting stuck on a too-low
 	 * time delta with no samples being sent due to round-off.
@@ -520,8 +527,16 @@ SR_PRIV int demo_prepare_data(int fd, int revents, void *cb_data)
 		return G_SOURCE_REMOVE;
 	}
 	devc->sent_samples += samples_todo;
+	devc->sent_frame_samples += samples_todo;
 	devc->spent_us += todo_us;
 
+#if (SAMPLES_PER_FRAME > 0) /* Avoid "comparison >= 0 always true" warning. */
+	if (devc->sent_frame_samples >= SAMPLES_PER_FRAME) {
+		std_session_send_frame_end(sdi);
+		devc->sent_frame_samples = 0;
+	}
+#endif
+
 	if ((devc->limit_samples > 0 && devc->sent_samples >= devc->limit_samples)
 			|| (limit_us > 0 && devc->spent_us >= limit_us)) {
 
@@ -540,10 +555,10 @@ SR_PRIV int demo_prepare_data(int fd, int revents, void *cb_data)
 		sr_dbg("Requested number of samples reached.");
 		sr_dev_acquisition_stop(sdi);
 	} else {
-		if (SAMPLES_PER_FRAME > 0) {
-			std_session_send_frame_end(sdi);
+#if (SAMPLES_PER_FRAME > 0)
+		if (devc->sent_frame_samples == 0)
 			std_session_send_frame_begin(sdi);
-		}
+#endif
 	}
 
 	return G_SOURCE_CONTINUE;
diff --git a/src/hardware/demo/protocol.h b/src/hardware/demo/protocol.h
index 53ad043b..f1c66711 100644
--- a/src/hardware/demo/protocol.h
+++ b/src/hardware/demo/protocol.h
@@ -41,6 +41,7 @@ struct dev_context {
 	uint64_t limit_samples;
 	uint64_t limit_msec;
 	uint64_t sent_samples;
+	uint64_t sent_frame_samples; /* Number of samples that were sent for current frame. */
 	int64_t start_us;
 	int64_t spent_us;
 	uint64_t step;