Index: trunk/psModules/src/detrend/pmFlatField.c
===================================================================
--- trunk/psModules/src/detrend/pmFlatField.c	(revision 13591)
+++ trunk/psModules/src/detrend/pmFlatField.c	(revision 15664)
@@ -77,5 +77,6 @@
         for (int i = 0; i < inImage->numCols; i++) { \
             ps##TYPE flatValue = flatImage->data.TYPE[j + yOffset][i + xOffset]; \
-            if (flatValue <= 0.0 || (flatMask && flatMask->data.U8[j + yOffset][i + xOffset])) { \
+            if (!isfinite(flatValue) || flatValue <= 0.0 ||
+                (flatMask && flatMask->data.U8[j + yOffset][i + xOffset])) { \
                 if (inMask) { \
                     inMask->data.PS_TYPE_MASK_DATA[j][i] |= badFlat; \