diff --git a/src/LIB/SURCOUCHE/src/mode_netcdf.f90 b/src/LIB/SURCOUCHE/src/mode_netcdf.f90
index bde8bc8cfe8776ad6a56ae2c9176f4d0f3b169cd..5449f9d3e6d06cc49b19d0c8c70a4b0ca77bec02 100644
--- a/src/LIB/SURCOUCHE/src/mode_netcdf.f90
+++ b/src/LIB/SURCOUCHE/src/mode_netcdf.f90
@@ -2413,10 +2413,19 @@ TZFIELD%CMNHNAME = TRIM(YVARNAME)
 !
 ! Model beginning date (TDTMOD%TDATE) is used as the reference date
 ! Reference time is set to 0.
-TZREF = TDTMOD
-TZREF%TIME = 0.
+IF (.NOT.ASSOCIATED(TDTMOD)) THEN
+  CALL PRINT_MSG(NVERB_WARNING,'IO','IO_WRITE_FIELD_NC4_T0',TRIM(TPFILE%CNAME)// &
+                 ': '//TRIM(TZFIELD%CMNHNAME)//': DTMOD is not associated and not known. Reference date set to 2000/01/01')
+  TZREF%TDATE%YEAR  = 2000
+  TZREF%TDATE%MONTH = 1
+  TZREF%TDATE%DAY   = 1
+  TZREF%TIME        = 0.
+ELSE
+  TZREF = TDTMOD
+  TZREF%TIME = 0.
+END IF
 WRITE(YUNITS,'( "seconds since ",I4.4,"-",I2.2,"-",I2.2," 00:00:00 +0:00" )') &
-      TDTMOD%TDATE%YEAR, TDTMOD%TDATE%MONTH, TDTMOD%TDATE%DAY
+      TZREF%TDATE%YEAR, TZREF%TDATE%MONTH, TZREF%TDATE%DAY
 TZFIELD%CUNITS = TRIM(YUNITS)
 !
 IF (TPFIELD%LTIMEDEP) &