Index: trunk/psModules/src/imcombine/pmSubtractionStamps.c
===================================================================
--- trunk/psModules/src/imcombine/pmSubtractionStamps.c	(revision 15219)
+++ trunk/psModules/src/imcombine/pmSubtractionStamps.c	(revision 15220)
@@ -70,4 +70,7 @@
     if (!mask) {
         return true;
+    }
+    if (x < 0 || x >= mask->numCols || y < 0 || y >= mask->numRows) {
+        return false;
     }
     return (mask->data.PS_TYPE_MASK_DATA[y][x] & (PM_SUBTRACTION_MASK_BORDER |