diff --git a/output/output_gnuplot.c b/output/output_gnuplot.c
index 4c887cbc..2bc19b39 100644
--- a/output/output_gnuplot.c
+++ b/output/output_gnuplot.c
@@ -34,11 +34,14 @@ struct context {
 const char *gnuplot_header = "\
 # Sample data in space-separated columns format usable by gnuplot\n\
 #\n\
-# Generated by: %s on %s\n\
-# Comment: Acquisition with %d/%d probes at %s\n\
+# Generated by: %s on %s\n%s\
 # Timescale: %d %s\n\
 # Column assignment:\n%s\n";
 
+const char *gnuplot_header_comment = "\
+# Comment: Acquisition with %d/%d probes at %s\n";
+
+
 static int init(struct output *o)
 {
 /* Maximum header length */
@@ -51,7 +54,7 @@ static int init(struct output *o)
 	unsigned int i;
 	int b, num_probes;
 	char *c, *samplerate_s;
-	char wbuf[1000];
+	char wbuf[1000], comment[128];
 
 	ctx = malloc(sizeof(struct context));
 	if (ctx == NULL)
@@ -74,11 +77,17 @@ static int init(struct output *o)
 		return SIGROK_ERR_MALLOC;
 	num_probes = g_slist_length(o->device->probes);
 	/* TODO: Handle num_probes == 0, too many probes, etc. */
-	samplerate = *((uint64_t *) o->device->plugin->get_device_info(
-			o->device->plugin_index, DI_CUR_SAMPLERATE));
-
-	if ((samplerate_s = sigrok_samplerate_string(samplerate)) == NULL)
-		return -1; /* FIXME */
+	if (o->device->plugin) {
+		samplerate = *((uint64_t *) o->device->plugin->get_device_info(
+				o->device->plugin_index, DI_CUR_SAMPLERATE));
+		if ((samplerate_s = sigrok_samplerate_string(samplerate)) == NULL)
+			return SIGROK_ERR;
+		snprintf(comment, 127, gnuplot_header_comment, ctx->num_enabled_probes,
+			     num_probes, samplerate_s);
+		free(samplerate_s);
+	}
+	else
+		comment[0] = '\0';
 
 	/* Columns / channels */
 	wbuf[0] = '\0';
@@ -90,10 +99,7 @@ static int init(struct output *o)
 	/* TODO: date: File or signals? Make y/n configurable. */
 	/* TODO: Timescale */
 	b = snprintf(ctx->header, MAX_HEADER_LEN, gnuplot_header,
-		     PACKAGE_STRING, "TODO", ctx->num_enabled_probes,
-		     num_probes, samplerate_s, 1, "ns", (char *)&wbuf);
-
-	free(samplerate_s);
+		     PACKAGE_STRING, "TODO", comment, 1, "ns", (char *)&wbuf);
 
 	/* TODO: Handle snprintf errors. */
 
diff --git a/output/output_text.c b/output/output_text.c
index 82487df0..05a368f0 100644
--- a/output/output_text.c
+++ b/output/output_text.c
@@ -100,17 +100,25 @@ static int init(struct output *o, int default_spl)
 	else
 		ctx->samples_per_line = default_spl;
 
-	ctx->header = malloc(512);
-	num_probes = g_slist_length(o->device->probes);
-	samplerate = *((uint64_t *) o->device->plugin->get_device_info(
-			o->device->plugin_index, DI_CUR_SAMPLERATE));
-	snprintf(ctx->header, 512, "Acquisition with %d/%d probes at ",
-		 ctx->num_enabled_probes, num_probes);
+	if (o->device->plugin) {
+		ctx->header = malloc(512);
+		num_probes = g_slist_length(o->device->probes);
+		samplerate = *((uint64_t *) o->device->plugin->get_device_info(
+				o->device->plugin_index, DI_CUR_SAMPLERATE));
+		snprintf(ctx->header, 512, "Acquisition with %d/%d probes at ",
+			 ctx->num_enabled_probes, num_probes);
 
-	if ((samplerate_s = sigrok_samplerate_string(samplerate)) == NULL)
-		return -1; /* FIXME */
-	snprintf(ctx->header + strlen(ctx->header), 512, "%s\n", samplerate_s);
-	free(samplerate_s);
+		if ((samplerate_s = sigrok_samplerate_string(samplerate)) == NULL)
+			return -1; /* FIXME */
+		snprintf(ctx->header + strlen(ctx->header), 512, "%s\n", samplerate_s);
+		free(samplerate_s);
+	} else {
+		/*
+		 * device has no plugin: this is just a dummy device, the data
+		 * comes from a file.
+		 */
+		ctx->header = NULL;
+	}
 
 	ctx->linebuf_len = ctx->samples_per_line * 2;
 	ctx->linebuf = calloc(1, num_probes * ctx->linebuf_len);
diff --git a/output/output_vcd.c b/output/output_vcd.c
index a147f5a9..fdb27ccc 100644
--- a/output/output_vcd.c
+++ b/output/output_vcd.c
@@ -34,8 +34,7 @@ struct context {
 
 const char *vcd_header = "\
 $date\n  %s\n$end\n\
-$version\n  %s\n$end\n\
-$comment\n  Acquisition with %d/%d probes at %s\n$end\n\
+$version\n  %s\n$end\n%s\
 $timescale\n  %i %s\n$end\n\
 $scope module %s $end\n\
 %s\
@@ -43,6 +42,10 @@ $upscope $end\n\
 $enddefinitions $end\n\
 $dumpvars\n";
 
+const char *vcd_header_comment = "\
+$comment\n  Acquisition with %d/%d probes at %s\n$end\n";
+
+
 static int init(struct output *o)
 {
 /* Maximum header length */
@@ -54,7 +57,7 @@ static int init(struct output *o)
 	uint64_t samplerate;
 	int i, b, num_probes;
 	char *c, *samplerate_s;
-	char wbuf[1000];
+	char wbuf[1000], comment[128];
 
 	ctx = malloc(sizeof(struct context));
 	if (ctx == NULL)
@@ -76,12 +79,19 @@ static int init(struct output *o)
 	if (ctx->header == NULL)
 		return SIGROK_ERR_MALLOC;
 	num_probes = g_slist_length(o->device->probes);
-	/* TODO: Handle num_probes == 0, too many probes, etc. */
-	samplerate = *((uint64_t *) o->device->plugin->get_device_info(
-			o->device->plugin_index, DI_CUR_SAMPLERATE));
 
-	if ((samplerate_s = sigrok_samplerate_string(samplerate)) == NULL)
-		return -1; /* FIXME */
+	if (o->device->plugin) {
+		/* TODO: Handle num_probes == 0, too many probes, etc. */
+		samplerate = *((uint64_t *) o->device->plugin->get_device_info(
+				o->device->plugin_index, DI_CUR_SAMPLERATE));
+		if ((samplerate_s = sigrok_samplerate_string(samplerate)) == NULL)
+			return SIGROK_ERR;
+		snprintf(comment, 127, vcd_header_comment, ctx->num_enabled_probes,
+				num_probes, samplerate_s);
+		free(samplerate_s);
+	}
+	else
+		comment[0] = '\0';
 
 	/* Wires / channels */
 	wbuf[0] = '\0';
@@ -93,12 +103,9 @@ static int init(struct output *o)
 
 	/* TODO: Date: File or signals? Make y/n configurable. */
 	b = snprintf(ctx->header, MAX_HEADER_LEN, vcd_header, "TODO: Date",
-		     PACKAGE_STRING, ctx->num_enabled_probes, num_probes,
-		     samplerate_s, 1, "ns", PACKAGE, (char *)&wbuf);
+			PACKAGE_STRING, comment, 1, "ns", PACKAGE, (char *)&wbuf);
 	/* TODO: Handle snprintf errors. */
 
-	free(samplerate_s);
-
 	ctx->prevbits = calloc(sizeof(int), num_probes);
 	if (ctx->prevbits == NULL)
 		return SIGROK_ERR_MALLOC;