Index: /trunk/psModules/src/camera/pmFPAMaskWeight.c
===================================================================
--- /trunk/psModules/src/camera/pmFPAMaskWeight.c	(revision 20748)
+++ /trunk/psModules/src/camera/pmFPAMaskWeight.c	(revision 20749)
@@ -491,6 +491,6 @@
     for (int i = 0; i < num; i++) {
         float measuredSig = PS_SQR(source->data.F32[i] / stdev); // Measured significance
-        ratio->data.F32[i] = guess->data.F32[i] / measuredSig;
-        if (source->data.F32[i] <= 0.0 || !isfinite(ratio->data.F32[i])) {
+        ratio->data.F32[i] = measuredSig / guess->data.F32[i];
+        if (guess->data.F32[i] <= 0.0 || source->data.F32[i] <= 0.0 || !isfinite(ratio->data.F32[i])) {
             photMask->data.PS_TYPE_MASK_DATA[i] = 0xFF;
         }