diff --git a/constants/geos_constants.h b/constants/geos_constants.h
index 3f2624ade9..edc298b41e 100644
--- a/constants/geos_constants.h
+++ b/constants/geos_constants.h
@@ -19,6 +19,8 @@
 
 character(len=18), public, parameter :: constants_version = 'FMSConstants: GEOS'
 
+!--- temporary definition for backwards compatibility
+real(kind=RKIND), public, parameter :: small_fac = 1._r8_kind
 
 !--- Spherical coordinate conversion constants
 real(kind=r8_kind), public, parameter :: PI_8 = 3.14159265358979323846_r8_kind  !< Ratio of circle circumference to diameter [N/A]
diff --git a/constants/gfdl_constants.h b/constants/gfdl_constants.h
index 17ec5d74e8..9e0b8812a1 100644
--- a/constants/gfdl_constants.h
+++ b/constants/gfdl_constants.h
@@ -19,6 +19,9 @@
 
 character(len=18), public, parameter :: constants_version = 'FMSConstants: GFDL'
 
+!--- temporary definition for backwards compatibility
+real(kind=RKIND), public, parameter :: small_fac = 1._r8_kind
+
 !--- Spherical coordinate conversion constants
 real(kind=r8_kind), public, parameter :: PI_8 = 3.14159265358979323846_r8_kind  !< Ratio of circle circumference to diameter [N/A]
 real(kind=RKIND),   public, parameter :: PI   = PI_8                            !< Ratio of circle circumference to diameter [N/A]
diff --git a/constants/gfs_constants.h b/constants/gfs_constants.h
index 171d31c95a..b732f6d43a 100644
--- a/constants/gfs_constants.h
+++ b/constants/gfs_constants.h
@@ -19,6 +19,9 @@
 
 character(len=18), public, parameter :: constants_version = 'FMSConstants: GFS '
 
+!--- temporary definition for backwards compatibility
+real(kind=RKIND), public, parameter :: small_fac = 1._r8_kind
+
 !--- Spherical coordinate conversion constants
 real(kind=r8_kind), public, parameter :: PI_8 = 3.1415926535897931_r8_kind    !< Ratio of circle circumference to diameter [N/A]
 real(kind=RKIND),   public, parameter :: PI   = PI_8                          !< Ratio of circle circumference to diameter [N/A]