Index: /trunk/psModules/src/detrend/pmFlatField.c
===================================================================
--- /trunk/psModules/src/detrend/pmFlatField.c	(revision 21532)
+++ /trunk/psModules/src/detrend/pmFlatField.c	(revision 21533)
@@ -43,5 +43,5 @@
 
     // Using i,j for image; x,y for flat.
-    for (int j = rowStart, y = yOffset; j < rowStop; j++, y++) {
+    for (int j = rowStart, y = rowStart + yOffset; j < rowStop; j++, y++) {
         for (int i = 0, x = xOffset; i < numCols; i++, x++) {
             float flatValue = 1.0 / flatImage->data.F32[y][x];