diff --git a/packages/extraterm-font-ligatures/src/processors/6-3.ts b/packages/extraterm-font-ligatures/src/processors/6-3.ts
index 347358ad..893aa546 100644
--- a/packages/extraterm-font-ligatures/src/processors/6-3.ts
+++ b/packages/extraterm-font-ligatures/src/processors/6-3.ts
@@ -1,6 +1,5 @@
-import { ChainingContextualSubstitutionTable, Lookup } from '../tables.js';
+import { ChainingContextualSubstitutionTable, CoverageTable, Lookup } from '../tables.js';
 import { LookupTree, LookupTreeEntry } from '../types.js';
-
 import { listGlyphsByIndex } from './coverage.js';
 import { processInputPosition, processLookaheadPosition, processBacktrackPosition, getInputTree,
   EntryMeta } from './helper.js';
@@ -40,16 +39,18 @@ export function buildTree(table: ChainingContextualSubstitutionTable.Format3, lo
       );
     }
 
-    for (const coverage of table.lookaheadCoverage) {
+    if (table.lookaheadCoverage.length > 0) {
+      const glyphsByIndex = coverageTablesToGlyphsByIndex(table.lookaheadCoverage);
       currentEntries = processLookaheadPosition(
-        listGlyphsByIndex(coverage).map(glyph => glyph.glyphId),
+        glyphsByIndex,
         currentEntries
       );
     }
 
-    for (const coverage of table.backtrackCoverage) {
+    if (table.backtrackCoverage.length > 0) {
+      const glyphsByIndex = coverageTablesToGlyphsByIndex(table.backtrackCoverage);
       currentEntries = processBacktrackPosition(
-        listGlyphsByIndex(coverage).map(glyph => glyph.glyphId),
+        glyphsByIndex,
         currentEntries
       );
     }
@@ -69,6 +70,13 @@ export function buildTree(table: ChainingContextualSubstitutionTable.Format3, lo
       };
     }
   }
-
   return result;
 }
+
+function coverageTablesToGlyphsByIndex(tables: CoverageTable[]): (number | [number, number])[] {
+  let glyphsByIndex: (number | [number, number])[] = [];
+  for (const coverage of tables) {
+    glyphsByIndex = glyphsByIndex.concat(listGlyphsByIndex(coverage).map(glyph => glyph.glyphId));
+  }
+  return glyphsByIndex;
+}
diff --git a/packages/extraterm-font-ligatures/src/processors/coverage.ts b/packages/extraterm-font-ligatures/src/processors/coverage.ts
index 5d8606c6..ffc7d054 100644
--- a/packages/extraterm-font-ligatures/src/processors/coverage.ts
+++ b/packages/extraterm-font-ligatures/src/processors/coverage.ts
@@ -25,7 +25,12 @@ export default function getCoverageGlyphIndex(table: CoverageTable, glyphId: num
   }
 }
 
-export function listGlyphsByIndex(table: CoverageTable): { glyphId: number | [number, number]; index: number; }[] {
+export interface GlyphIdIndex {
+  glyphId: number | [number, number];
+  index: number;
+}
+
+export function listGlyphsByIndex(table: CoverageTable): GlyphIdIndex[] {
   switch (table.format) {
     case 1:
       return table.glyphs.map((glyphId, index) => ({ glyphId, index }));
diff --git a/packages/extraterm-font-ligatures/src/processors/helper.ts b/packages/extraterm-font-ligatures/src/processors/helper.ts
index 0e6dbc6f..da65c4ac 100644
--- a/packages/extraterm-font-ligatures/src/processors/helper.ts
+++ b/packages/extraterm-font-ligatures/src/processors/helper.ts
@@ -21,7 +21,7 @@ export function processInputPosition(
       individual: new Map<number, LookupTreeEntry>(),
       range: []
     };
-    for (const glyph of glyphs) {
+    for (const glyph of dedupGlyphs(glyphs)) {
       nextEntries.push(...getInputTree(
         currentEntry.entry.forward,
         lookupRecords,
@@ -44,7 +44,7 @@ export function processLookaheadPosition(
 ): EntryMeta[] {
   const nextEntries: EntryMeta[] = [];
   for (const currentEntry of currentEntries) {
-    for (const glyph of glyphs) {
+    for (const glyph of dedupGlyphs(glyphs)) {
       const entry: LookupTreeEntry = {};
       if (!currentEntry.entry.forward) {
         currentEntry.entry.forward = {
@@ -76,8 +76,9 @@ export function processBacktrackPosition(
   currentEntries: EntryMeta[]
 ): EntryMeta[] {
   const nextEntries: EntryMeta[] = [];
+
   for (const currentEntry of currentEntries) {
-    for (const glyph of glyphs) {
+    for (const glyph of dedupGlyphs(glyphs)) {
       const entry: LookupTreeEntry = {};
       if (!currentEntry.entry.reverse) {
         currentEntry.entry.reverse = {
@@ -100,10 +101,42 @@ export function processBacktrackPosition(
       }
     }
   }
-
   return nextEntries;
 }
 
+function dedupGlyphs(glyphs: (number | [number, number])[]): (number | [number, number])[] {
+  if (glyphs.length < 2) {
+    return glyphs;
+  }
+
+  const result: (number | [number, number])[] = [];
+  const singleGlyphs = new Set<number>();
+  const pairGlyphs = new Set<[number, number]>();
+
+  for (const glyph of glyphs) {
+    if (Array.isArray(glyph)) {
+      let found = false;
+      for (const pair of pairGlyphs) {
+        if (pair[0] === glyph[0] && pair[1] === glyph[1]) {
+          found = true;
+          break;
+        }
+      }
+      if (!found) {
+        result.push(glyph);
+        pairGlyphs.add(glyph);
+      }
+
+    } else {
+      if (!singleGlyphs.has(glyph)) {
+        result.push(glyph);
+        singleGlyphs.add(glyph);
+      }
+    }
+  }
+  return result;
+}
+
 export function getInputTree(tree: LookupTree, substitutions: SubstitutionLookupRecord[], lookups: Lookup[], inputIndex: number, glyphId: number | [number, number]): { entry: LookupTreeEntry; substitution: number | null; }[] {
   const result: { entry: LookupTreeEntry; substitution: number | null; }[] = [];
   if (!Array.isArray(glyphId)) {