diff --git a/src/features/featureQuery.js b/src/features/featureQuery.js
index 4aead842..8c945baa 100644
--- a/src/features/featureQuery.js
+++ b/src/features/featureQuery.js
@@ -149,15 +149,27 @@ function chainingSubstitutionFormat3(contextParams, subtable) {
             const lookupListIndex = lookupRecord.lookupListIndex;
             const lookupTable = this.getLookupByIndex(lookupListIndex);
             for (let s = 0; s < lookupTable.subtables.length; s++) {
-                const subtable = lookupTable.subtables[s];
-                const lookup = this.getLookupMethod(lookupTable, subtable);
-                const substitutionType = this.getSubstitutionType(lookupTable, subtable);
+                let subtable = lookupTable.subtables[s];
+                let lookup;
+                let substitutionType = this.getSubstitutionType(lookupTable, subtable);
+
+                if (substitutionType === '71') {
+                    // This is an extension subtable, so lookup the target subtable
+                    substitutionType = this.getSubstitutionType(subtable, subtable.extension);
+                    lookup = this.getLookupMethod(subtable, subtable.extension);
+                    subtable = subtable.extension;
+                } else {
+                    lookup = this.getLookupMethod(lookupTable, subtable);
+                }
+
                 if (substitutionType === '12') {
                     for (let n = 0; n < inputLookups.length; n++) {
                         const glyphIndex = contextParams.get(n);
                         const substitution = lookup(glyphIndex);
                         if (substitution) substitutions.push(substitution);
                     }
+                } else {
+                    throw new Error(`Substitution type ${substitutionType} is not supported in chaining substitution`);
                 }
             }
         }
@@ -367,9 +379,19 @@ FeatureQuery.prototype.lookupFeature = function (query) {
         const lookupTable = lookups[l];
         const subtables = this.getLookupSubtables(lookupTable);
         for (let s = 0; s < subtables.length; s++) {
-            const subtable = subtables[s];
-            const substType = this.getSubstitutionType(lookupTable, subtable);
-            const lookup = this.getLookupMethod(lookupTable, subtable);
+            let subtable = subtables[s];
+            let substType = this.getSubstitutionType(lookupTable, subtable);
+            let lookup;
+
+            if (substType === '71') {
+                // This is an extension subtable, so lookup the target subtable
+                substType = this.getSubstitutionType(subtable, subtable.extension);
+                lookup = this.getLookupMethod(subtable, subtable.extension);
+                subtable = subtable.extension;
+            } else {
+                lookup = this.getLookupMethod(lookupTable, subtable);
+            }
+
             let substitution;
             switch (substType) {
                 case '11':
diff --git a/test/tables/gsub.js b/test/tables/gsub.js
index a788c5e8..f3ce0fa2 100644
--- a/test/tables/gsub.js
+++ b/test/tables/gsub.js
@@ -213,7 +213,28 @@ describe('tables/gsub.js', function() {
     // TODO (no example in the doc from Microsoft)
 
     //// Lookup type 7 ////////////////////////////////////////////////////////
-    // TODO (no example in the doc from Microsoft)
+    it('can parse lookup7 subtable format 1', function() {
+
+        const data =
+            '00 01' +                    // substFormat
+            '00 01' +                    // extensionLookupType
+            '00 00 00 08' +              //	extensionOffset
+            '0001 0006 00C0   0002 0001 004E 0058 0000' // data equal to that from the lookup1 substFormat 1 test
+            ;
+        const parsed = parseLookup(7, data);
+        assert.deepEqual(parsed, {
+            extension: { // object equal to that from the lookup1 substFormat 1 test
+                substFormat: 1,
+                coverage: {
+                    format: 2,
+                    ranges: [{ start: 0x4e, end: 0x58, index: 0 }]
+                },
+                deltaGlyphId: 0xc0
+            },
+            lookupType: 1,
+            substFormat: 1
+        });
+    });
 
     //// Lookup type 8 ////////////////////////////////////////////////////////
     it('can parse lookup8', function() {