diff --git a/unittest/fortran/test_fortran_properties.f90 b/unittest/fortran/test_fortran_properties.f90
index b68794ce14..4f22321076 100644
--- a/unittest/fortran/test_fortran_properties.f90
+++ b/unittest/fortran/test_fortran_properties.f90
@@ -72,10 +72,12 @@ FUNCTION f_lammps_get_last_error_message(errmesg, errlen) BIND(C)
    CALL lmp%get_last_error_message(buffer, status)
    f_lammps_get_last_error_message = status
    ! and copy to C style string
+   errmesg(1:errlen) = c_null_char
    DO i=1, errlen
       errmesg(i) = buffer(i:i)
       IF (buffer(i:i) == c_null_char) EXIT
    END DO
+   errmesg(errlen) = c_null_char
    DEALLOCATE(buffer)
 END FUNCTION f_lammps_get_last_error_message