diff --git a/lib/autotune/index.js b/lib/autotune/index.js
index 40531f7c..5e7a88d2 100644
--- a/lib/autotune/index.js
+++ b/lib/autotune/index.js
@@ -143,16 +143,16 @@ function tuneAllTheThings (inputs) {
     var ratios = [];
     var count = 0;
     for (var i=0; i < ISFGlucose.length; ++i) {
-       deviation = parseFloat(ISFGlucose[i].deviation);
-       deviations.push(deviation);
-       BGI = parseFloat(ISFGlucose[i].BGI);
-       BGIs.push(BGI);
-       avgDelta = parseFloat(ISFGlucose[i].avgDelta);
-       avgDeltas.push(avgDelta);
-       ratio = 1 + deviation / BGI;
-       //console.error("Deviation:",deviation,"BGI:",BGI,"avgDelta:",avgDelta,"ratio:",ratio);
-       ratios.push(ratio);
-       count++;
+        deviation = parseFloat(ISFGlucose[i].deviation);
+        deviations.push(deviation);
+        BGI = parseFloat(ISFGlucose[i].BGI);
+        BGIs.push(BGI);
+        avgDelta = parseFloat(ISFGlucose[i].avgDelta);
+        avgDeltas.push(avgDelta);
+        ratio = 1 + deviation / BGI;
+        //console.error("Deviation:",deviation,"BGI:",BGI,"avgDelta:",avgDelta,"ratio:",ratio);
+        ratios.push(ratio);
+        count++;
     }
     avgDeltas.sort(function(a, b){return a-b});
     BGIs.sort(function(a, b){return a-b});
@@ -161,9 +161,13 @@ function tuneAllTheThings (inputs) {
     p50deviation = percentile(deviations, 0.50);
     p50BGI = percentile(BGIs, 0.50);
     p50ratios = Math.round( percentile(ratios, 0.50) * 1000)/1000;
-
-    // calculate what adjustments to ISF would have been necessary to bring median deviation to zero
-    fullNewISF = ISF * p50ratios;
+    if (count < 5) {
+        // leave ISF unchanged if fewer than 5 ISF data points
+        fullNewISF = ISF;
+    } else {
+        // calculate what adjustments to ISF would have been necessary to bring median deviation to zero
+        fullNewISF = ISF * p50ratios;
+    }
     fullNewISF = Math.round( fullNewISF * 1000 ) / 1000;
     // and apply 10% of that adjustment
     var newISF = ( 0.9 * ISF ) + ( 0.1 * fullNewISF );