diff --git a/.changeset/eighty-olives-count.md b/.changeset/eighty-olives-count.md
new file mode 100644
index 0000000..1a77354
--- /dev/null
+++ b/.changeset/eighty-olives-count.md
@@ -0,0 +1,5 @@
+---
+'@trustnxt/c2pa-ts': patch
+---
+
+Use two underscores for ingredient thumbnail assertion suffix
diff --git a/src/manifest/assertions/ThumbnailAssertion.ts b/src/manifest/assertions/ThumbnailAssertion.ts
index 1f0ba60..3fecfb7 100644
--- a/src/manifest/assertions/ThumbnailAssertion.ts
+++ b/src/manifest/assertions/ThumbnailAssertion.ts
@@ -100,7 +100,7 @@ export class ThumbnailAssertion extends Assertion {
             assertion.label = AssertionLabels.thumbnailPrefix + imageType;
         } else {
             assertion.label =
-                AssertionLabels.ingredientThumbnailPrefix + (suffix ? '_' + suffix : '') + '.' + imageType;
+                AssertionLabels.ingredientThumbnailPrefix + (suffix ? '__' + suffix : '') + '.' + imageType;
         }
         return assertion;
     }