diff --git a/src/predict/predict_class.js b/src/predict/predict_class.js
index 85f30ca..b33c07d 100644
--- a/src/predict/predict_class.js
+++ b/src/predict/predict_class.js
@@ -161,6 +161,11 @@ class Predict {
     //find index of y peak
     const { peak , peakIndex } = this.getLocalPeak(curve.y);
 
+    // Guard against invalid peakIndex (e.g. empty array returns -1)
+    if (peakIndex < 0 || peakIndex >= curve.x.length) {
+      return { yPeak: null, x: null, xProcent: null };
+    }
+
     // scale the x value to procentual value
     const yPeak = peak;
     const x = curve.x[peakIndex];