diff --git a/clock.c b/clock.c
index 17c9687..c59046a 100644
--- a/clock.c
+++ b/clock.c
@@ -801,19 +801,18 @@ static void clock_remove_port(struct clock *c, struct port *p)
 }
 
 struct clock *clock_create(enum clock_type type, struct config *config,
-			   int phc_index)
+			   const char *phc_device)
 {
 	enum timestamp_type timestamping =
 		config_get_int(config, NULL, "time_stamping");
 	int fadj = 0, max_adj = 0, sw_ts = timestamping == TS_SOFTWARE ? 1 : 0;
 	enum servo_type servo = config_get_int(config, NULL, "clock_servo");
+	int phc_index, required_modes = 0;
 	struct clock *c = &the_clock;
-	int required_modes = 0;
 	struct port *p;
 	unsigned char oui[OUI_LEN];
 	char phc[32], *tmp;
-	struct interface *udsif = &c->uds_interface;
-	struct interface *iface = STAILQ_FIRST(&config->interfaces);
+	struct interface *iface, *udsif = &c->uds_interface;
 	struct timespec ts;
 	int sfl;
 
@@ -936,6 +935,29 @@ struct clock *clock_create(enum clock_type type, struct config *config,
 	}
 
 	iface = STAILQ_FIRST(&config->interfaces);
+
+	/* determine PHC Clock index */
+	if (config_get_int(config, NULL, "free_running")) {
+		phc_index = -1;
+	} else if (config_get_int(config, NULL, "time_stamping") == TS_SOFTWARE ||
+		   config_get_int(config, NULL, "time_stamping") == TS_LEGACY_HW) {
+		phc_index = -1;
+	} else if (phc_device) {
+		if (1 != sscanf(phc_device, "/dev/ptp%d", &phc_index)) {
+			pr_err("bad ptp device string");
+			return NULL;
+		}
+	} else if (iface->ts_info.valid) {
+		phc_index = iface->ts_info.phc_index;
+	} else {
+		pr_err("PTP device not specified and automatic determination"
+		       " is not supported. Please specify PTP device.");
+		return NULL;
+	}
+	if (phc_index >= 0) {
+		pr_info("selected /dev/ptp%d as PTP clock", phc_index);
+	}
+
 	if (generate_clock_identity(&c->dds.clockIdentity, iface->name)) {
 		pr_err("failed to generate a clock identity");
 		return NULL;
diff --git a/clock.h b/clock.h
index d4a57e9..fcd9328 100644
--- a/clock.h
+++ b/clock.h
@@ -78,12 +78,12 @@ struct config *clock_config(struct clock *c);
  *
  * @param type         Specifies which type of clock to create.
  * @param config       Pointer to the configuration database.
- * @param phc_index    PTP hardware clock device to use.
- *                     Pass -1 to select CLOCK_REALTIME.
+ * @param phc_device   PTP hardware clock device to use. Pass NULL for automatic
+ *                     selection based on the network interface.
  * @return             A pointer to the single global clock instance.
  */
 struct clock *clock_create(enum clock_type type, struct config *config,
-			   int phc_index);
+			   const char *phc_device);
 
 /**
  * Obtains a clock's default data set.
diff --git a/ptp4l.c b/ptp4l.c
index c3694b0..a87e7e6 100644
--- a/ptp4l.c
+++ b/ptp4l.c
@@ -73,11 +73,9 @@ static void usage(char *progname)
 int main(int argc, char *argv[])
 {
 	char *config = NULL, *req_phc = NULL, *progname;
-	int c, err = -1;
-	struct interface *iface;
+	int c, err = -1, print_level;
 	struct clock *clock = NULL;
 	struct config *cfg;
-	int phc_index = -1, print_level;
 
 	if (handle_term_signals())
 		return -1;
@@ -197,33 +195,8 @@ int main(int argc, char *argv[])
 		goto out;
 	}
 
-	/* determine PHC Clock index */
-	iface = STAILQ_FIRST(&cfg->interfaces);
-	if (config_get_int(cfg, NULL, "free_running")) {
-		phc_index = -1;
-	} else if (config_get_int(cfg, NULL, "time_stamping") == TS_SOFTWARE ||
-		   config_get_int(cfg, NULL, "time_stamping") == TS_LEGACY_HW) {
-		phc_index = -1;
-	} else if (req_phc) {
-		if (1 != sscanf(req_phc, "/dev/ptp%d", &phc_index)) {
-			fprintf(stderr, "bad ptp device string\n");
-			goto out;
-		}
-	} else if (iface->ts_info.valid) {
-		phc_index = iface->ts_info.phc_index;
-	} else {
-		fprintf(stderr, "ptp device not specified and\n"
-			        "automatic determination is not\n"
-			        "supported. please specify ptp device\n");
-		goto out;
-	}
-
-	if (phc_index >= 0) {
-		pr_info("selected /dev/ptp%d as PTP clock", phc_index);
-	}
-
 	clock = clock_create(cfg->n_interfaces > 1 ? CLOCK_TYPE_BOUNDARY :
-			     CLOCK_TYPE_ORDINARY, cfg, phc_index);
+			     CLOCK_TYPE_ORDINARY, cfg, req_phc);
 	if (!clock) {
 		fprintf(stderr, "failed to create a clock\n");
 		goto out;