diff --git a/openbsc/src/osmo-nitb/bsc_hack.c b/openbsc/src/osmo-nitb/bsc_hack.c
index 0b360dc..e3e8927 100644
--- a/openbsc/src/osmo-nitb/bsc_hack.c
+++ b/openbsc/src/osmo-nitb/bsc_hack.c
@@ -299,6 +299,19 @@
 #endif
 	bsc_api_init(bsc_gsmnet, msc_bsc_api());
 
+	/*
+	 * For osmo-nitb, skip TCH/F for now, because otherwise dyn TS
+	 * always imply the possibility to have a mix of TCH/F and
+	 * TCH/H channels; if two phones request a TCH/F and a TCH/H,
+	 * respectively, they cannot call each other. If we deny TCH/F,
+	 * they will both fall back to TCH/H, and dynamic channels are
+	 * usable. See http://osmocom.org/issues/1778.
+	 *
+	 * A third-party MSC may well be able to handle a TCH/H TCH/F
+	 * mismatch.
+	 */
+	bsc_gsmnet->dyn_ts_allow_tch_f = false;
+
 	/* start control interface after reading config for
 	 * ctrl_vty_get_bind_addr() */
 	LOGP(DNM, LOGL_NOTICE, "CTRL at %s %d\n",