diff --git a/src/core/evaluator.js b/src/core/evaluator.js
index 3a97ebbbe..209a58152 100644
--- a/src/core/evaluator.js
+++ b/src/core/evaluator.js
@@ -1750,7 +1750,7 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
       // the differences array only contains adobe standard or symbol set names,
       // in pratice it seems better to always try to create a toUnicode
       // map based of the default encoding.
-      var toUnicode, charcode;
+      var toUnicode, charcode, glyphName;
       if (!properties.composite /* is simple font */) {
         toUnicode = [];
         var encoding = properties.defaultEncoding.slice();
@@ -1758,12 +1758,18 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
         // Merge in the differences array.
         var differences = properties.differences;
         for (charcode in differences) {
-          encoding[charcode] = differences[charcode];
+          glyphName = differences[charcode];
+          if (glyphName === '.notdef') {
+            // Skip .notdef to prevent rendering errors, e.g. boxes appearing
+            // where there should be spaces (fixes issue5256.pdf).
+            continue;
+          }
+          encoding[charcode] = glyphName;
         }
         var glyphsUnicodeMap = getGlyphsUnicode();
         for (charcode in encoding) {
           // a) Map the character code to a character name.
-          var glyphName = encoding[charcode];
+          glyphName = encoding[charcode];
           // b) Look up the character name in the Adobe Glyph List (see the
           //    Bibliography) to obtain the corresponding Unicode value.
           if (glyphName === '') {
diff --git a/test/pdfs/.gitignore b/test/pdfs/.gitignore
index d0b08ac30..18459a896 100644
--- a/test/pdfs/.gitignore
+++ b/test/pdfs/.gitignore
@@ -13,6 +13,7 @@
 !issue3214.pdf
 !issue4665.pdf
 !issue4684.pdf
+!issue5256.pdf
 !issue5801.pdf
 !issue5946.pdf
 !issue5972.pdf
diff --git a/test/pdfs/issue5256.pdf b/test/pdfs/issue5256.pdf
new file mode 100644
index 000000000..f6d3cf249
Binary files /dev/null and b/test/pdfs/issue5256.pdf differ
diff --git a/test/test_manifest.json b/test/test_manifest.json
index ac342b40c..b15f03633 100644
--- a/test/test_manifest.json
+++ b/test/test_manifest.json
@@ -1387,6 +1387,13 @@
       "link": true,
       "type": "eq"
     },
+    {  "id": "issue5256",
+       "file": "pdfs/issue5256.pdf",
+       "md5": "9383e17ced31f9afc940fb7898df8e68",
+       "rounds": 1,
+       "link": false,
+       "type": "eq"
+    },
     {  "id": "issue6360",
        "file": "pdfs/issue6360.pdf",
        "md5": "58c5455ffd84b1c07ad2d0fa90cd5e26",