diff --git a/src/core/colorspace.js b/src/core/colorspace.js
index 149cdf9840d23..7da5daa9df850 100644
--- a/src/core/colorspace.js
+++ b/src/core/colorspace.js
@@ -462,7 +462,7 @@ class ColorSpace {
         case "I":
         case "Indexed":
           baseCS = this._parse(cs[1], xref, resources, pdfFunctionFactory);
-          const hiVal = xref.fetchIfRef(cs[2]) + 1;
+          const hiVal = Math.max(0, Math.min(xref.fetchIfRef(cs[2]), 255));
           const lookup = xref.fetchIfRef(cs[3]);
           return new IndexedCS(baseCS, hiVal, lookup);
         case "Separation":
@@ -630,9 +630,8 @@ class IndexedCS extends ColorSpace {
   constructor(base, highVal, lookup) {
     super("Indexed", 1);
     this.base = base;
-    this.highVal = highVal;
 
-    const length = base.numComps * highVal;
+    const length = base.numComps * (highVal + 1);
     this.lookup = new Uint8Array(length);
 
     if (lookup instanceof BaseStream) {