Index: trunk/psModules/src/imcombine/pmSubtraction.c
===================================================================
--- trunk/psModules/src/imcombine/pmSubtraction.c	(revision 29772)
+++ trunk/psModules/src/imcombine/pmSubtraction.c	(revision 29777)
@@ -1375,8 +1375,4 @@
     // Calculate covariances
     // This can be fairly involved, so we only do it for a small number of instances
-        if (!out1->covariance) {
-            psError(PM_ERR_PROG, false, "psImageCovarianceAverage returned NULL.");
-            return false;
-        }
     float position[NUM_COVAR_POS] = { -1.0, -0.5, 0.0, +0.5, +1.0 }; // Positions for covariance calculations
     // Enable threads for covariance calculation, since we're not threading on top of it