diff --git a/callouts/77-nm-probe-modem-capabilities.rules b/callouts/77-nm-probe-modem-capabilities.rules
index e1d702ed34..261a5351d3 100644
--- a/callouts/77-nm-probe-modem-capabilities.rules
+++ b/callouts/77-nm-probe-modem-capabilities.rules
@@ -4,7 +4,7 @@ ACTION!="add|change", GOTO="nm_modem_probe_end"
 SUBSYSTEM!="tty", GOTO="nm_modem_probe_end"
 KERNEL!="tty*", GOTO="nm_modem_probe_end"
 
-DRIVERS=="option|sierra|hso|serial_cs|cdc_acm", IMPORT{program}="nm-modem-probe --delay 2000 --export $tempnode"
+DRIVERS=="option|sierra|hso|serial_cs|cdc_acm", IMPORT{program}="nm-modem-probe --delay 3000 --export $tempnode"
 
 LABEL="nm_modem_probe_end"
 
diff --git a/callouts/nm-modem-probe.c b/callouts/nm-modem-probe.c
index c7d5b11574..fd77089d93 100644
--- a/callouts/nm-modem-probe.c
+++ b/callouts/nm-modem-probe.c
@@ -281,22 +281,88 @@ parse_gmm (const char *buf)
 	return gsm ? MODEM_CAP_GSM : 0;
 }
 
-static int modem_probe_caps(int fd)
+static int
+g_timeval_subtract (GTimeVal *result, GTimeVal *x, GTimeVal *y)
+{
+	int nsec;
+
+	/* Perform the carry for the later subtraction by updating y. */
+	if (x->tv_usec < y->tv_usec) {
+		nsec = (y->tv_usec - x->tv_usec) / G_USEC_PER_SEC + 1;
+		y->tv_usec -= G_USEC_PER_SEC * nsec;
+		y->tv_sec += nsec;
+	}
+	if (x->tv_usec - y->tv_usec > G_USEC_PER_SEC) {
+		nsec = (x->tv_usec - y->tv_usec) / G_USEC_PER_SEC;
+		y->tv_usec += G_USEC_PER_SEC * nsec;
+		y->tv_sec -= nsec;
+	}
+
+	/* Compute the time remaining to wait.
+	   tv_usec is certainly positive. */
+	result->tv_sec = x->tv_sec - y->tv_sec;
+	result->tv_usec = x->tv_usec - y->tv_usec;
+
+	/* Return 1 if result is negative. */
+	return x->tv_sec < y->tv_sec;
+}
+
+static int modem_probe_caps(int fd, glong timeout_ms)
 {
 	const char *gcap_responses[] = { GCAP_TAG, NULL };
 	const char *terminators[] = { "OK", "ERROR", "ERR", NULL };
 	char *reply = NULL;
-	int idx, term_idx, ret = 0;
+	int idx = -1, term_idx = -1, ret = 0;
+	gboolean try_ati = FALSE;
+	GTimeVal start, end;
+	gboolean send_success;
 
-	if (!modem_send_command (fd, "AT+GCAP\r\n"))
-		return -1;
+	/* If a delay was specified, start a bit later */
+	if (timeout_ms > 500) {
+		g_usleep (500000);
+		timeout_ms -= 500;
+	}
 
-	idx = modem_wait_reply (fd, 3, gcap_responses, terminators, &term_idx, &reply);
-	if (0 == term_idx && 0 == idx) {
-		/* Success */
-		verbose ("GCAP response: %s", reply);
-		ret = parse_gcap (reply);
-	} else if (1 == term_idx || 2 == term_idx) {
+	/* Standard response timeout case */
+	timeout_ms += 3000;
+
+	while (timeout_ms > 0) {
+		GTimeVal diff;
+
+		g_get_current_time (&start);
+
+		idx = term_idx = 0;
+		send_success = modem_send_command (fd, "AT+GCAP\r\n");
+		if (send_success)
+			idx = modem_wait_reply (fd, 2, gcap_responses, terminators, &term_idx, &reply);
+
+		g_get_current_time (&end);
+		g_timeval_subtract (&diff, &end, &start);
+		timeout_ms -= (diff.tv_sec * 1000) + (diff.tv_usec / 1000);
+
+		if (!send_success)
+			continue;
+
+		if (0 == term_idx && 0 == idx) {
+			/* Success */
+			verbose ("GCAP response: %s", reply);
+			ret = parse_gcap (reply);
+			break;
+		} else if (0 == term_idx && -1 == idx) {
+			/* Just returned "OK" but no GCAP (Sierra) */
+			try_ati = TRUE;
+			break;
+		} else if (1 == term_idx || 2 == term_idx) {
+			try_ati = TRUE;
+		} else
+			verbose ("timed out waiting for GCAP reply (idx %d, term_idx %d)", idx, term_idx);
+		g_free (reply);
+		reply = NULL;
+		g_usleep (100000);
+		timeout_ms -= 100;
+	}
+
+	if (!ret && try_ati) {
 		const char *ati_responses[] = { GCAP_TAG, NULL };
 
 		/* Many cards (ex Sierra 860 & 875) won't accept AT+GCAP but
@@ -314,8 +380,7 @@ static int modem_probe_caps(int fd)
 				ret = parse_gcap (reply);
 			}
 		}
-	} else
-		verbose ("timed out waiting for GCAP reply (idx %d, term_idx %d)", idx, term_idx);
+	}
 
 	g_free (reply);
 	reply = NULL;
@@ -441,11 +506,6 @@ main(int argc, char *argv[])
 		delay_ms = (guint32) tmp;
 	}
 
-	if (delay_ms) {
-		verbose ("waiting %ums before probing", delay_ms);
-		g_usleep (delay_ms * 1000);
-	}
-
 	fd = open (device, O_RDWR | O_EXCL | O_NONBLOCK);
 	if (fd < 0) {
 		g_printerr ("open(%s) failed: %d\n", device, errno);
@@ -470,7 +530,7 @@ main(int argc, char *argv[])
 	attrs.c_cflag |= (B9600 | CS8 | CREAD | PARENB);
 	
 	tcsetattr (fd, TCSANOW, &attrs);
-	caps = modem_probe_caps (fd);
+	caps = modem_probe_caps (fd, delay_ms);
 	tcsetattr (fd, TCSANOW, &orig);
 
 	if (caps < 0) {