diff --git a/targets/PROJECTS/GENERIC-LTE-EPC/CONF/testing_enb.conf b/targets/PROJECTS/GENERIC-LTE-EPC/CONF/testing_enb.conf
index d26ebcd590..6f6ff63438 100644
--- a/targets/PROJECTS/GENERIC-LTE-EPC/CONF/testing_enb.conf
+++ b/targets/PROJECTS/GENERIC-LTE-EPC/CONF/testing_enb.conf
@@ -263,7 +263,7 @@ RUs = (
          max_pdschReferenceSignalPower = -27;
          max_rxgain                    = 118;
          eNB_instances  = [0];
-         clock_src = "external";
+         clock_src = "internal";
     }
 );  
 
diff --git a/targets/PROJECTS/GENERIC-LTE-EPC/CONF/testing_gnb.conf b/targets/PROJECTS/GENERIC-LTE-EPC/CONF/testing_gnb.conf
index c46ea98ec2..8bf788566a 100644
--- a/targets/PROJECTS/GENERIC-LTE-EPC/CONF/testing_gnb.conf
+++ b/targets/PROJECTS/GENERIC-LTE-EPC/CONF/testing_gnb.conf
@@ -264,7 +264,7 @@ RUs = (
          max_pdschReferenceSignalPower = -27;
          max_rxgain                    = 114;
          eNB_instances  = [0];
-         clock_src = "external";
+         clock_src = "internal";
     }
 );