diff --git a/src/ctphase/ctphase.cpp b/src/ctphase/ctphase.cpp
index 34e1bd2..4d5da3b 100644
--- a/src/ctphase/ctphase.cpp
+++ b/src/ctphase/ctphase.cpp
@@ -633,16 +633,30 @@ void ctphase::phase_events(GCTAObservation*   obs,
                              const std::string& evtname,
                              const std::string& gtiname)
 {
-    // Write header into logger
-    log_header3(NORMAL, "Events phasing");
-
     // Get CTA event list pointer
     GCTAEventList* list =
         static_cast<GCTAEventList*>(const_cast<GEvents*>(obs->events()));
     
+    GCTAEventAtom* event = (*list)[0];
+    
+    // Print a warning into the log file if there are some precision concerns
+    double dt = std::abs(event->time() - m_phase.mjd());
+    if (((m_phase.f1() * dt) > 1.0e8) ||
+        (m_phase.f2() * dt * dt) > 1.0e8) {
+        log_string(NORMAL,"*** WARNING ***");
+        log_string(NORMAL,"   Values supplied for reference MJD and/or f1 and/or f2");
+        log_string(NORMAL,"   are large and may result in numerical precision issues.");
+        log_string(NORMAL,"   Consider using an ephemeris derived from a date closer");
+        log_string(NORMAL,"   to the data being analyzed.");
+        log_value(NORMAL, "     Observation ID", obs->obs_id());
+        log_value(NORMAL, "     Reference MJD", m_phase.mjd().mjd());
+        log_value(NORMAL, "     First event MJD", event->time().mjd());
+        log_string(NORMAL,"*** WARNING ***");
+    }
+    
     for (int evnt=0; evnt<list->size(); evnt++) {
         // Get the next event
-        GCTAEventAtom* event = (*list)[evnt];
+        event = (*list)[evnt];
         
         // Get the event time
         GTime time = event->time();
diff --git a/src/ctphase/ctphase.par b/src/ctphase/ctphase.par
index c3bfd80..bf62251 100644
--- a/src/ctphase/ctphase.par
+++ b/src/ctphase/ctphase.par
@@ -24,11 +24,11 @@ prefix, s, h, "phased_",,, "Prefix for event lists in observation definition XML
 #
 # Phase information parameters
 #=====================
-mjd,    r, a, 52400,,, "Reference MJD for phase information"
-f0,     r, a, 1,,, "Frequency at reference MJD [Hz]"
-f1,     r, a, -0.2,,, "First freq. derivative at reference MJD [s^-1]"
-f2,     r, a, 0,,, "Second freq. derivative at reference MJD [s^-2]"
+mjd,    r, a, 51544.5,,, "Reference MJD for phase information"
 p0,     r, a, 0.1,0.0,1.0, "Phase at reference MJD"
+f0,     r, a, 1,,, "Frequency at reference MJD [Hz]"
+f1,     r, a, 0.0,,, "First freq. derivative at reference MJD [s^-1]"
+f2,     r, a, 0.0,,, "Second freq. derivative at reference MJD [s^-2]"
 
 #
 # Standard parameters
diff --git a/test/test_ctphase.py b/test/test_ctphase.py
index d02646c..2412ff4 100644
--- a/test/test_ctphase.py
+++ b/test/test_ctphase.py
@@ -71,7 +71,7 @@ class Test(test):
         # Setup ctphase command
         cmd = ctphase+' inobs="'+self._events+'"'+ \
                        ' outobs="ctphase_cmd1.fits"'+ \
-                       ' p0=0.1 mjd=52400'+ \
+                       ' p0=0.1 mjd=51544.5'+ \
                        ' f0=0.1 f1=0. f2=0.'+ \
                        ' logfile="ctphase_cmd1.log" chatter=1'
 
@@ -89,7 +89,7 @@ class Test(test):
         # Setup ctphase command
         cmd = ctphase+' inobs="event_file_that_does_not_exist.fits"'+ \
                        ' outobs="ctphase_cmd2.fits"'+ \
-                       ' p0=0.1 mjd=52400'+ \
+                       ' p0=0.1 mjd=51544.5'+ \
                        ' f0=0.1 f1=0. f2=0.'+ \
                        ' logfile="ctphase_cmd2.log" chatter=1'
 
@@ -137,9 +137,9 @@ class Test(test):
         # Now set ctphase parameters
         phase['inobs']   = self._events
         phase['p0']      = 0.
-        phase['mjd']     = 52400
+        phase['mjd']     = 51544.5
         phase['f0']      = 1.
-        phase['f1']      = -0.2
+        phase['f1']      = 0.0
         phase['f2']      = 0.
         phase['outobs']  = 'ctphase_py1.fits'
         phase['logfile'] = 'ctphase_py1.log'
@@ -158,18 +158,18 @@ class Test(test):
 
         # Execute copy of ctphase tool again, now with a negative value
         # of initial phase to test for invalid parameter value
+        self.test_try('Test invalid parameter value')
         try:
-            self.test_try('Test invalid parameter value')
-            cpy_phase['p0']      = -0.5
-            cpy_phase['mjd']     = 52400
+            cpy_phase['mjd']     = 51544.5
             cpy_phase['f0']      = 1.
-            cpy_phase['f1']      = -0.2
+            cpy_phase['f1']      = 0.2
             cpy_phase['f2']      = 0.
             cpy_phase['outobs']  = 'ctphase_py2.fits'
             cpy_phase['logfile'] = 'ctphase_py2.log'
             cpy_phase['chatter'] = 3
             cpy_phase['publish'] = True
             cpy_phase.logFileOpen()  # Needed to get a new log file
+            cpy_phase['p0']      = -0.5
             cpy_phase.execute()
             self.test_try_failure('Exception not thrown')
         except ValueError: