Index: trunk/ppImage/src/ppImageDetrendReadout.c
===================================================================
--- trunk/ppImage/src/ppImageDetrendReadout.c	(revision 25930)
+++ trunk/ppImage/src/ppImageDetrendReadout.c	(revision 26629)
@@ -89,4 +89,24 @@
             psFree (binning);
         }
+
+        // Check that the gain is set
+        float gain = psMetadataLookupF32(NULL, input->parent->concepts, "CELL.GAIN"); // Gain for cell
+        if (!isfinite(gain)) {
+            psMetadata *recipe = psMetadataLookupMetadata(NULL, config->recipes, RECIPE_NAME); // Recipe
+            psAssert(recipe, "Should be there!");
+            bool override = psMetadataLookupBool(NULL, recipe, "GAIN.OVERRIDE"); // Override the bad gain?
+            if (override) {
+                psWarning("CELL.GAIN is not set for readout (%d,%d,%d) --- setting to unity.",
+                          view->chip, view->cell, view->readout);
+                psMetadataItem *item = psMetadataLookup(input->parent->concepts, "CELL.GAIN"); // Gain item
+                psAssert(item, "Should be there!");
+                item->data.F32 = 1.0;
+            } else {
+                psError(PS_ERR_BAD_PARAMETER_VALUE, false, "CELL.GAIN is not set for readout (%d,%d,%d)",
+                        view->chip, view->cell, view->readout);
+                return false;
+            }
+        }
+
         pmReadoutGenerateVariance(input, noiseImage, true);
         psFree (noiseImage);