diff --git a/src/libcode/vx_summary/summary_obs.cc b/src/libcode/vx_summary/summary_obs.cc
index 6267a5e78c..a8fd7d6c24 100644
--- a/src/libcode/vx_summary/summary_obs.cc
+++ b/src/libcode/vx_summary/summary_obs.cc
@@ -368,6 +368,15 @@ vector< SummaryCalc* > SummaryObs::getSummaryCalculators(const TimeSummaryInfo &
       }
       else if (type == "sum") {
         calculators.push_back(new SummaryCalcSum);
+
+        // Check for vld_thresh = 1.0
+        if (!is_eq(info.vld_thresh, 1.0)) {
+           mlog << Warning << "\nIn the \"time_summary\" dictionary, "
+		<< "consider setting \"vld_thresh\" (" << info.vld_thresh
+	       	<< ") to 1.0 for the \"sum\" type to better handle "
+	        << "missing data.\n\n";
+	}
+
       }
       else if (type[0] == 'p') {
         calculators.push_back(new SummaryCalcPercentile(type));