diff --git a/src/browser/ColorManager.test.ts b/src/browser/ColorManager.test.ts
index dfcc9ec8f3..3fbd92f1c4 100644
--- a/src/browser/ColorManager.test.ts
+++ b/src/browser/ColorManager.test.ts
@@ -315,14 +315,14 @@ describe('ColorManager', () => {
         extendedAnsi: DEFAULT_ANSI_COLORS.map(a => a.css).slice().reverse()
       });
 
-      for (let ansiColor = 16; ansiColor <= 255; ansiColor++){
+      for (let ansiColor = 16; ansiColor <= 255; ansiColor++) {
         assert.equal(cm.colors.ansi[ansiColor].css, DEFAULT_ANSI_COLORS[255 + 16 - ansiColor].css);
       }
     });
 
     it('should set one extended ansi colors and keep the other default', () => {
       cm.setTheme({
-        extendedAnsi: [ '#ffffff' ]
+        extendedAnsi: ['#ffffff']
       });
 
       assert.equal(cm.colors.ansi[16].css, '#ffffff');
diff --git a/src/browser/ColorManager.ts b/src/browser/ColorManager.ts
index 1d1b567229..84e5d58d44 100644
--- a/src/browser/ColorManager.ts
+++ b/src/browser/ColorManager.ts
@@ -168,9 +168,9 @@ export class ColorManager implements IColorManager {
     this.colors.ansi[14] = this._parseColor(theme.brightCyan, DEFAULT_ANSI_COLORS[14]);
     this.colors.ansi[15] = this._parseColor(theme.brightWhite, DEFAULT_ANSI_COLORS[15]);
     if (theme.extendedAnsi) {
-      const colorCount = Math.max(theme.extendedAnsi.length + 16, 256);
-      for (let i = 16; i < colorCount; i++) {
-        this.colors.ansi[i] = this._parseColor(theme.extendedAnsi[i - 16], DEFAULT_ANSI_COLORS[i]);
+      const colorCount = Math.min(this.colors.ansi.length - 16, theme.extendedAnsi.length);
+      for (let i = 0; i < colorCount; i++) {
+        this.colors.ansi[i + 16] = this._parseColor(theme.extendedAnsi[i], DEFAULT_ANSI_COLORS[i + 16]);
       }
     }
     // Clear our the cache