Index: trunk/psModules/src/imcombine/pmSubtractionMask.c
===================================================================
--- trunk/psModules/src/imcombine/pmSubtractionMask.c	(revision 19164)
+++ trunk/psModules/src/imcombine/pmSubtractionMask.c	(revision 20832)
@@ -137,4 +137,6 @@
     // footprint's distance of those (within 'footprint').
 
+    bool oldThreads = psImageConvolveSetThreads(true); // Old value of threading for psImageConvolve
+
     if (!psImageConvolveMask(mask, mask, PM_SUBTRACTION_MASK_BAD_1,
                              PM_SUBTRACTION_MASK_CONVOLVE_1,
@@ -151,4 +153,6 @@
         return NULL;
     }
+
+    psImageConvolveSetThreads(oldThreads);
 
     return mask;