diff --git a/src/evolution.F90 b/src/evolution.F90
index d22bb88..c6d9675 100644
--- a/src/evolution.F90
+++ b/src/evolution.F90
@@ -843,6 +843,9 @@ module evolution
 !
     use coordinates   , only : im, jm, km
     use equations     , only : nv, pvars, cvars
+#ifdef IBM
+    use, intrinsic :: ieee_arithmetic
+#endif /* IBM */
 
 ! include external variables
 !
@@ -882,12 +885,21 @@ module evolution
         do j = 1, jm
           do i = 1, im
             do p = 1, nv
+#ifdef IBM
+              if (ieee_is_nan(pdata%u(p,i,j,k))) then
+                print *, 'U NaN:', cvars(p), pdata%meta%id, i, j, k
+              end if
+              if (ieee_is_isnan(pdata%q(p,i,j,k))) then
+                print *, 'Q NaN:', pvars(p), pdata%meta%id, i, j, k
+              end if
+#else /* IBM */
               if (isnan(pdata%u(p,i,j,k))) then
                 print *, 'U NaN:', cvars(p), pdata%meta%id, i, j, k
               end if
               if (isnan(pdata%q(p,i,j,k))) then
                 print *, 'Q NaN:', pvars(p), pdata%meta%id, i, j, k
               end if
+#endif /* IBM */
             end do ! p = 1, nv
           end do ! i = 1, im
         end do ! j = 1, jm