diff --git a/src/core/evaluator.js b/src/core/evaluator.js
index df5b1c1d7..2376799c3 100644
--- a/src/core/evaluator.js
+++ b/src/core/evaluator.js
@@ -2350,6 +2350,10 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
           }
         }
 
+        const firstChar = (dict.get('FirstChar') || 0);
+        const lastChar = (dict.get('LastChar') || (composite ? 0xFFFF : 0xFF));
+        hash.update(`${firstChar}-${lastChar}`);
+
         var toUnicode = dict.get('ToUnicode') || baseDict.get('ToUnicode');
         if (isStream(toUnicode)) {
           var stream = toUnicode.str || toUnicode;
diff --git a/test/pdfs/.gitignore b/test/pdfs/.gitignore
index 259a95710..de9e5edcc 100644
--- a/test/pdfs/.gitignore
+++ b/test/pdfs/.gitignore
@@ -76,6 +76,7 @@
 !issue10388_reduced.pdf
 !issue10438_reduced.pdf
 !issue10529.pdf
+!issue10665_reduced.pdf
 !bad-PageLabels.pdf
 !decodeACSuccessive.pdf
 !filled-background.pdf
diff --git a/test/pdfs/issue10665_reduced.pdf b/test/pdfs/issue10665_reduced.pdf
new file mode 100644
index 000000000..49d96ec4b
Binary files /dev/null and b/test/pdfs/issue10665_reduced.pdf differ
diff --git a/test/test_manifest.json b/test/test_manifest.json
index c188d388e..884d50fc3 100644
--- a/test/test_manifest.json
+++ b/test/test_manifest.json
@@ -2564,6 +2564,13 @@
        "link": false,
        "type": "eq"
     },
+    {  "id": "issue10665",
+       "file": "pdfs/issue10665_reduced.pdf",
+       "md5": "4c8938c808153f6b3840e8a5eb68b804",
+       "rounds": 1,
+       "link": false,
+       "type": "eq"
+    },
     {  "id": "issue1466",
       "file": "pdfs/issue1466.pdf",
       "md5": "8a8877432e5bb10cfd50d60488d947bb",