diff --git a/sources/user_problem.F90 b/sources/user_problem.F90
index 6b4b377..b37252b 100644
--- a/sources/user_problem.F90
+++ b/sources/user_problem.F90
@@ -1111,9 +1111,9 @@ module user_problem
       fc(:) = (abs(yc(:)) - yabs) / adec
 
       do j = 1, nn
-        if (fc(j) >= 0.0d+00) then
-          if (fc(j) <= 1.0d+00) then
-            fr = fa * sin(5.0d-01 * pi * yc(j))**2
+        if (fc(j) > 0.0d+00) then
+          if (fc(j) < 1.0d+00) then
+            fr = fa * sin(5.0d-01 * pi * fc(j))**2
           else
             fr = fa
           end if