Index: /branches/eam_branches/ipp-20211108/psModules/src/imcombine/pmStack.c
===================================================================
--- /branches/eam_branches/ipp-20211108/psModules/src/imcombine/pmStack.c	(revision 41957)
+++ /branches/eam_branches/ipp-20211108/psModules/src/imcombine/pmStack.c	(revision 41958)
@@ -1756,5 +1756,9 @@
 	      int P75 = 0.75*nGoodClip + Nlo;
 	      float rawSigma = 0.74*(pixelData->data.F32[P75] - pixelData->data.F32[P25]);
-	      varValue = PS_SQR(rawSigma) / (float) nGoodClip; // sigma_mean = sigma_meas / sqrt(Nmeas) -> var_mean = var_meas / Nmeas
+	      varValue = PS_MIN(9e7, PS_SQR(rawSigma) / (float) nGoodClip); // sigma_mean = sigma_meas / sqrt(Nmeas) -> var_mean = var_meas / Nmeas
+	      // XXX the upper limit of 9e7 is set to match the output
+	      // format (STK_UNIONS) which can only represent values up to that limit.
+	      // perhaps it would be better to saturate the output image in psFits
+	      // rather than here.  
 	    }