diff --git a/config.c b/config.c
index 08e29a2..b8f2bdb 100644
--- a/config.c
+++ b/config.c
@@ -91,6 +91,10 @@ static void scan_line(char *s, struct config *cfg)
 
 		pod->transportSpecific = u8 << 4;
 
+	} else if (1 == sscanf(s, " assume_two_step %u", &val)) {
+
+		*cfg->assume_two_step = val ? 1 : 0;
+
 	} else if (1 == sscanf(s, " tx_timestamp_retries %u", &val)) {
 
 		if (val > 0)
diff --git a/config.h b/config.h
index 8fde9c1..fb22341 100644
--- a/config.h
+++ b/config.h
@@ -25,6 +25,7 @@
 struct config {
 	struct defaultDS *dds;
 	struct port_defaults *pod;
+	int *assume_two_step;
 	int *tx_timestamp_retries;
 	int *rx_timestamp_l2only;
 	double *pi_proportional_const;
diff --git a/msg.h b/msg.h
index f479e9c..d737ee2 100644
--- a/msg.h
+++ b/msg.h
@@ -284,6 +284,11 @@ void msg_put(struct ptp_message *m);
  */
 int msg_sots_missing(struct ptp_message *m);
 
+/**
+ * Work around buggy 802.1AS switches.
+ */
+extern int assume_two_step;
+
 /**
  * Test whether a message is one-step message.
  * @param m  Message to test.
@@ -291,6 +296,8 @@ int msg_sots_missing(struct ptp_message *m);
  */
 static inline Boolean one_step(struct ptp_message *m)
 {
+	if (assume_two_step)
+		return 0;
 	return !field_is_set(m, 0, TWO_STEP);
 }
 
diff --git a/ptp4l.c b/ptp4l.c
index 52ba480..deadf62 100644
--- a/ptp4l.c
+++ b/ptp4l.c
@@ -30,6 +30,7 @@
 
 #define DEFAULT_PHC "/dev/ptp0"
 
+int assume_two_step;
 int sk_tx_retries = 2, sk_prefer_layer2 = 0; /*see sk.c*/
 double configured_pi_kp, configured_pi_ki; /*see pi.c*/
 extern unsigned char ptp_dst_mac[]; /*see raw.c*/
@@ -219,6 +220,7 @@ int main(int argc, char *argv[])
 
 	cfg_settings.dds = &ds;
 	cfg_settings.pod = &pod;
+	cfg_settings.assume_two_step = &assume_two_step;
 	cfg_settings.tx_timestamp_retries = &sk_tx_retries;
 	cfg_settings.rx_timestamp_l2only = &sk_prefer_layer2;
 	cfg_settings.pi_proportional_const = &configured_pi_kp;