diff --git a/public-trunk/Transceiver52M/UHDDevice.cpp b/public-trunk/Transceiver52M/UHDDevice.cpp
index a5b1f0c..b86dd33 100644
--- a/public-trunk/Transceiver52M/UHDDevice.cpp
+++ b/public-trunk/Transceiver52M/UHDDevice.cpp
@@ -32,8 +32,6 @@
 #endif
 
 /*
-    use_ext_ref       - Enable external 10MHz clock reference
-
     master_clk_rt     - Master clock frequency - ignored if host resampling is
                         enabled
 
@@ -46,7 +44,6 @@
 
     tx_ampl           - Transmit amplitude must be between 0 and 1.0
 */
-const bool use_ext_ref = false;
 const double master_clk_rt = 52e6;
 const size_t smpl_buf_sz = (1 << 20);
 const float tx_ampl = .3;
@@ -426,6 +423,10 @@ bool uhd_device::open()
 		return false;
 	}
 
+#ifdef EXTREF
+	set_ref_clk(true);
+#endif
+
 	// Number of samples per over-the-wire packet
 	tx_spp = usrp_dev->get_device()->get_max_send_samps_per_packet();
 	rx_spp = usrp_dev->get_device()->get_max_recv_samps_per_packet();
@@ -445,9 +446,6 @@ bool uhd_device::open()
 	// Initialize and shadow gain values 
 	init_gains();
 
-	// Set reference clock
-	set_ref_clk(use_ext_ref);
-
 	// Print configuration
 	LOG(INFO) << "\n" << usrp_dev->get_pp_string();
 
diff --git a/public-trunk/configure.ac b/public-trunk/configure.ac
index 7b3424a..6a83482 100644
--- a/public-trunk/configure.ac
+++ b/public-trunk/configure.ac
@@ -67,6 +67,11 @@ AC_ARG_WITH(resamp, [
         [enable resampling for non-52MHz devices])
 ])
 
+AC_ARG_WITH(extref, [
+    AS_HELP_STRING([--with-extref],
+        [enable external reference on UHD devices])
+])
+
 AS_IF([test "x$with_usrp1" = "xyes"], [
     # Defines USRP_CFLAGS, USRP_INCLUDEDIR, and USRP_LIBS
     PKG_CHECK_MODULES(USRP, usrp > 3.1)
@@ -89,6 +94,10 @@ AS_IF([test "x$with_resamp" = "xyes"], [
     AC_DEFINE(RESAMPLE, 1, Define to 1 for resampling)
 ])
 
+AS_IF([test "x$with_extref" = "xyes"], [
+    AC_DEFINE(EXTREF, 1, Define to 1 for external reference)
+])
+
 AM_CONDITIONAL(RESAMPLE, [test "x$with_resamp" = "xyes"])
 AM_CONDITIONAL(UHD, [test "x$with_usrp1" != "xyes"])