diff --git a/interface/model/clm3_5/enkf_clm_mod.F90 b/interface/model/clm3_5/enkf_clm_mod.F90
index cb53f938..19861f13 100755
--- a/interface/model/clm3_5/enkf_clm_mod.F90
+++ b/interface/model/clm3_5/enkf_clm_mod.F90
@@ -25,6 +25,7 @@
 module enkf_clm_mod
 
   use iso_c_binding
+  use IEEE_ARITHMETIC, only: ieee_is_nan
 
 ! !USES:
   use shr_kind_mod    , only : r8 => shr_kind_r8, SHR_KIND_CL
@@ -445,7 +446,7 @@ subroutine update_clm(tstartcycle, mype) bind(C,name="update_clm")
                 swc(j,i)   = clm_statevec(cc+offset)
               endif
 
-              if (isnan(swc(j,i))) then
+              if (ieee_is_nan(swc(j,i))) then
                       swc(j,i) = watmin_set
                       print *, "WARNING: swc at j,i is nan: ", j, i
               endif
diff --git a/interface/model/eclm/enkf_clm_mod_5.F90 b/interface/model/eclm/enkf_clm_mod_5.F90
index 82fa382a..a866406f 100755
--- a/interface/model/eclm/enkf_clm_mod_5.F90
+++ b/interface/model/eclm/enkf_clm_mod_5.F90
@@ -25,6 +25,7 @@
 module enkf_clm_mod
 
   use iso_c_binding, only: c_int, c_double, c_char
+  use IEEE_ARITHMETIC, only: ieee_is_nan
 
 ! !USES:
   use shr_kind_mod    , only : r8 => shr_kind_r8, SHR_KIND_CL
@@ -740,7 +741,7 @@ subroutine update_clm_swc(tstartcycle, mype)
                   swc(j,i)   = swc_update
                 endif
 
-                if (isnan(swc(j,i))) then
+                if (ieee_is_nan(swc(j,i))) then
                   swc(j,i) = watmin_set
                   print *, "WARNING: swc at j,i is nan: ", j, i
                 endif