diff --git a/src/core/fonts.js b/src/core/fonts.js
index ca2c01179..aa40dbcaa 100644
--- a/src/core/fonts.js
+++ b/src/core/fonts.js
@@ -2651,6 +2651,25 @@ class Font {
             unicodeOrCharCode = MacRomanEncoding.indexOf(standardGlyphName);
           }
 
+          if (unicodeOrCharCode === undefined) {
+            // Not a valid glyph name, fallback to using the /ToUnicode map
+            // when no post-table exists (fixes issue13316_reduced.pdf).
+            if (
+              !properties.glyphNames &&
+              properties.hasIncludedToUnicodeMap &&
+              !(this.toUnicode instanceof IdentityToUnicodeMap)
+            ) {
+              const unicode = this.toUnicode.get(charCode);
+              if (unicode) {
+                unicodeOrCharCode = unicode.codePointAt(0);
+              }
+            }
+
+            if (unicodeOrCharCode === undefined) {
+              continue; // No valid glyph mapping found.
+            }
+          }
+
           for (let i = 0; i < cmapMappingsLength; ++i) {
             if (cmapMappings[i].charCode !== unicodeOrCharCode) {
               continue;
diff --git a/test/pdfs/.gitignore b/test/pdfs/.gitignore
index bc9a1dd8e..ee07ee273 100644
--- a/test/pdfs/.gitignore
+++ b/test/pdfs/.gitignore
@@ -240,6 +240,7 @@
 !issue4304.pdf
 !issue4379.pdf
 !issue4550.pdf
+!issue13316_reduced.pdf
 !issue4575.pdf
 !bug1011159.pdf
 !issue5734.pdf
diff --git a/test/pdfs/issue13316_reduced.pdf b/test/pdfs/issue13316_reduced.pdf
new file mode 100644
index 000000000..2ebbd1a5e
Binary files /dev/null and b/test/pdfs/issue13316_reduced.pdf differ
diff --git a/test/test_manifest.json b/test/test_manifest.json
index 1cf730d01..17dc5893b 100644
--- a/test/test_manifest.json
+++ b/test/test_manifest.json
@@ -4321,6 +4321,12 @@
       "lastPage": 4,
       "type": "load"
     },
+    {  "id": "issue13316",
+       "file": "pdfs/issue13316_reduced.pdf",
+       "md5": "f5821891cee29d8de8b65e1efd6f4ceb",
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "issue10519",
        "file": "pdfs/issue10519_reduced.pdf",
        "md5": "8a2dae43c0ef47b0734bedaaa24f8c09",