Index: /trunk/psModules/src/imcombine/pmSubtractionEquation.c
===================================================================
--- /trunk/psModules/src/imcombine/pmSubtractionEquation.c	(revision 26030)
+++ /trunk/psModules/src/imcombine/pmSubtractionEquation.c	(revision 26031)
@@ -1016,5 +1016,5 @@
             #define TOL 1.0e-5
             int normIndex = PM_SUBTRACTION_INDEX_NORM(kernels); // Index for normalisation
-            double norm = solution->data.F64[normIndex];        // Normalisation
+            double norm = fabs(solution->data.F64[normIndex]);  // Normalisation
             double thresh = norm * TOL;                         // Threshold for low parameters
             for (int i = 0; i < numKernels; i++) {