diff --git a/output/output_skeleton.c b/output/output_skeleton.c
index 6bd885f9..24cada4a 100644
--- a/output/output_skeleton.c
+++ b/output/output_skeleton.c
@@ -23,11 +23,9 @@
 
 
 
-static void init(struct output *o)
+static int init(struct output *o)
 {
-
-
-
+	return 0;
 }
 
 
diff --git a/output/output_text.c b/output/output_text.c
index 0507e02c..914e51fc 100644
--- a/output/output_text.c
+++ b/output/output_text.c
@@ -66,7 +66,7 @@ static void flush_linebufs(struct context *ctx, GSList *probes, char *outbuf)
 }
 
 
-static void init(struct output *o, int default_spl)
+static int init(struct output *o, int default_spl)
 {
 	struct context *ctx;
 	struct probe *probe;
@@ -109,6 +109,7 @@ static void init(struct output *o, int default_spl)
 	ctx->linebuf = calloc(1, num_probes * ctx->linebuf_len);
 	ctx->linevalues = calloc(1, num_probes);
 
+	return 0;
 }
 
 
@@ -137,10 +138,10 @@ static int event(struct output *o, int event_type, char **data_out, uint64_t *le
 }
 
 
-static void init_binary(struct output *o)
+static int init_binary(struct output *o)
 {
 
-	init(o, DEFAULT_BPL_BIN);
+	return init(o, DEFAULT_BPL_BIN);
 
 }
 
@@ -199,10 +200,10 @@ static int data_binary(struct output *o, char *data_in, uint64_t length_in, char
 }
 
 
-static void init_hex(struct output *o)
+static int init_hex(struct output *o)
 {
 
-	init(o, DEFAULT_BPL_BIN);
+	return init(o, DEFAULT_BPL_BIN);
 
 }
 
diff --git a/output/output_vcd.c b/output/output_vcd.c
index c9eba1bb..0d8d9d31 100644
--- a/output/output_vcd.c
+++ b/output/output_vcd.c
@@ -30,7 +30,6 @@ struct context {
 	char *probelist[65];
 	int *prevbits;
 	char *header;
-	char *data;
 };
 
 const char *vcd_header = "\
@@ -44,7 +43,7 @@ $upscope $end\n\
 $enddefinitions $end\n\
 $dumpvars\n";
 
-static void init(struct output *o)
+static int init(struct output *o)
 {
 /* Maximum header length */
 #define MAX_HEADER_LEN 2048
@@ -100,6 +99,8 @@ static void init(struct output *o)
 		     (char *)&sbuf, 1, "ns", PACKAGE, (char *)&wbuf);
 
 	ctx->prevbits = calloc(sizeof(int), num_probes);
+
+	return 0;
 }
 
 static int event(struct output *o, int event_type, char **data_out,
diff --git a/sigrok.h b/sigrok.h
index cf5cb61f..1d11aff7 100644
--- a/sigrok.h
+++ b/sigrok.h
@@ -99,7 +99,7 @@ struct output {
 struct output_format {
 	char *extension;
 	char *description;
-	void (*init) (struct output *o);
+	int (*init) (struct output *o);
 	int (*data) (struct output *o, char *data_in, uint64_t length_in,
 		     char **data_out, uint64_t *length_out);
 	int (*event) (struct output *o, int event_type, char **data_out,