diff --git a/src/core/evaluator.js b/src/core/evaluator.js
index 10cd2a963..3b8a4c9b2 100644
--- a/src/core/evaluator.js
+++ b/src/core/evaluator.js
@@ -1827,7 +1827,7 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
     extractDataStructures:
         function PartialEvaluator_extractDataStructures(dict, baseDict,
                                                         properties) {
-      var xref = this.xref;
+      let xref = this.xref, cidToGidBytes;
       // 9.10.2
       var toUnicode = (dict.get('ToUnicode') || baseDict.get('ToUnicode'));
       var toUnicodePromise = toUnicode ?
@@ -1846,7 +1846,7 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
 
         var cidToGidMap = dict.get('CIDToGIDMap');
         if (isStream(cidToGidMap)) {
-          properties.cidToGidMap = this.readCidToGidMap(cidToGidMap);
+          cidToGidBytes = cidToGidMap.getBytes();
         }
       }
 
@@ -1929,8 +1929,12 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
       return toUnicodePromise.then((toUnicode) => {
         properties.toUnicode = toUnicode;
         return this.buildToUnicode(properties);
-      }).then(function (toUnicode) {
+      }).then((toUnicode) => {
         properties.toUnicode = toUnicode;
+        if (cidToGidBytes) {
+          properties.cidToGidMap = this.readCidToGidMap(cidToGidBytes,
+                                                        toUnicode);
+        }
         return properties;
       });
     },
@@ -2146,18 +2150,17 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
       return Promise.resolve(null);
     },
 
-    readCidToGidMap: function PartialEvaluator_readCidToGidMap(cidToGidStream) {
+    readCidToGidMap(glyphsData, toUnicode) {
       // Extract the encoding from the CIDToGIDMap
-      var glyphsData = cidToGidStream.getBytes();
 
       // Set encoding 0 to later verify the font has an encoding
       var result = [];
       for (var j = 0, jj = glyphsData.length; j < jj; j++) {
         var glyphID = (glyphsData[j++] << 8) | glyphsData[j];
-        if (glyphID === 0) {
+        const code = j >> 1;
+        if (glyphID === 0 && !toUnicode.has(code)) {
           continue;
         }
-        var code = j >> 1;
         result[code] = glyphID;
       }
       return result;
diff --git a/src/core/fonts.js b/src/core/fonts.js
index f4d00ae8d..c519dd75d 100644
--- a/src/core/fonts.js
+++ b/src/core/fonts.js
@@ -1606,7 +1606,8 @@ var Font = (function FontClosure() {
         };
       }
 
-      function sanitizeMetrics(font, header, metrics, numGlyphs) {
+      function sanitizeMetrics(font, header, metrics, numGlyphs,
+                               dupFirstEntry) {
         if (!header) {
           if (metrics) {
             metrics.data = null;
@@ -1649,6 +1650,11 @@ var Font = (function FontClosure() {
           // the use of |numMissing * 2| when initializing the typed array.
           var entries = new Uint8Array(metrics.length + numMissing * 2);
           entries.set(metrics.data);
+          if (dupFirstEntry) {
+            // Set the sidebearing value of the duplicated glyph.
+            entries[metrics.length] = metrics.data[2];
+            entries[metrics.length + 1] = metrics.data[3];
+          }
           metrics.data = entries;
         }
       }
@@ -2366,7 +2372,8 @@ var Font = (function FontClosure() {
 
       // Ensure the hmtx table contains the advance width and
       // sidebearings information for numGlyphs in the maxp table
-      sanitizeMetrics(font, tables['hhea'], tables['hmtx'], numGlyphsOut);
+      sanitizeMetrics(font, tables['hhea'], tables['hmtx'], numGlyphsOut,
+                      dupFirstEntry);
 
       if (!tables['head']) {
         throw new FormatError('Required "head" table is not found');
diff --git a/test/pdfs/.gitignore b/test/pdfs/.gitignore
index 343eeef41..b704c9682 100644
--- a/test/pdfs/.gitignore
+++ b/test/pdfs/.gitignore
@@ -293,6 +293,7 @@
 !issue5540.pdf
 !issue5549.pdf
 !issue5475.pdf
+!issue10519_reduced.pdf
 !annotation-border-styles.pdf
 !IdentityToUnicodeMap_charCodeOf.pdf
 !PDFJS-9279-reduced.pdf
diff --git a/test/pdfs/issue10519_reduced.pdf b/test/pdfs/issue10519_reduced.pdf
new file mode 100644
index 000000000..a80ff5e2c
Binary files /dev/null and b/test/pdfs/issue10519_reduced.pdf differ
diff --git a/test/test_manifest.json b/test/test_manifest.json
index 20605a9b2..ecf7234d5 100644
--- a/test/test_manifest.json
+++ b/test/test_manifest.json
@@ -3126,6 +3126,12 @@
       "lastPage": 4,
       "type": "load"
     },
+    {  "id": "issue10519",
+       "file": "pdfs/issue10519_reduced.pdf",
+       "md5": "8a2dae43c0ef47b0734bedaaa24f8c09",
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "issue3061",
       "file": "pdfs/issue3061.pdf",
       "md5": "696a7cb1b194d095ca3f7861779a606b",