Index: /trunk/psModules/src/detrend/pmDetrendDB.c
===================================================================
--- /trunk/psModules/src/detrend/pmDetrendDB.c	(revision 31055)
+++ /trunk/psModules/src/detrend/pmDetrendDB.c	(revision 31056)
@@ -137,4 +137,19 @@
     psFree (realCamera);
 
+    // require a filter for certain types of detrends:
+    if ((options->type == PM_DETREND_TYPE_FLAT) && !options->filter) {
+        psError (PM_ERR_CONFIG, false, "requesting a FLAT-class of detrend without a filter");
+        goto failure;
+    }
+    if ((options->type == PM_DETREND_TYPE_FLATCORR) && !options->filter) {
+        psError (PM_ERR_CONFIG, false, "requesting a FLATCORR-class of detrend without a filter");
+        goto failure;
+    }
+    if ((options->type == PM_DETREND_TYPE_FRINGE) && !options->filter) {
+        psError (PM_ERR_CONFIG, false, "requesting a FRINGE-class of detrend without a filter");
+        goto failure;
+    }
+
+    // add the restrictions
     if (options->filter) {
         psStringAppend(&line, " -filter %s", options->filter);