diff --git a/src/core/evaluator.js b/src/core/evaluator.js
index 0ab0e524a..9b3f31167 100644
--- a/src/core/evaluator.js
+++ b/src/core/evaluator.js
@@ -4469,6 +4469,19 @@ class PartialEvaluator {
           hash.update(cidToGidMap.peekBytes());
         }
       }
+
+      if (type.name === "Type3") {
+        // Type3 fonts with the same metrics/encoding but different CharProcs
+        // must not be aliased, since their glyphs may render completely
+        // differently (e.g. one font uses SMask glyph programs, another uses
+        // plain paths, see issue 19634).
+        const charProcs = baseDict.get("CharProcs");
+        if (charProcs instanceof Dict) {
+          for (const [key, entry] of charProcs.getRawEntries()) {
+            hash.update(entry instanceof Ref ? `${key}\0${entry}` : key);
+          }
+        }
+      }
     }
 
     return {
diff --git a/test/pdfs/.gitignore b/test/pdfs/.gitignore
index 7d83280fe..7ba0239d7 100644
--- a/test/pdfs/.gitignore
+++ b/test/pdfs/.gitignore
@@ -900,3 +900,4 @@
 !issue7821.pdf
 !issue21068.pdf
 !recursiveCompositGlyf.pdf
+!issue19634.pdf
diff --git a/test/pdfs/issue19634.pdf b/test/pdfs/issue19634.pdf
new file mode 100644
index 000000000..cc5d38773
Binary files /dev/null and b/test/pdfs/issue19634.pdf differ
diff --git a/test/test_manifest.json b/test/test_manifest.json
index 992ad54aa..d83e9e493 100644
--- a/test/test_manifest.json
+++ b/test/test_manifest.json
@@ -14112,5 +14112,12 @@
     "md5": "e4e106d20e4af10d7a5f1a5da02db66f",
     "rounds": 1,
     "type": "eq"
+  },
+  {
+    "id": "issue19634",
+    "file": "pdfs/issue19634.pdf",
+    "md5": "ae33892db2a2421ec7c9c3e2aee07205",
+    "rounds": 1,
+    "type": "eq"
   }
 ]