diff --git a/src/protocol/tests/utils.rs b/src/protocol/tests/utils.rs
index 5dc895e2375c035bc85e36c53d9a2968a2f44ae8..4fcdf8f1ccf5bed0b8548b4590d393395a6194af 100644
--- a/src/protocol/tests/utils.rs
+++ b/src/protocol/tests/utils.rs
@@ -906,7 +906,7 @@ fn has_monomorph(ctx: TestCtx, definition_id: DefinitionId, serialized_monomorph
 
     full_buffer.push('[');
     let mut append_to_full_buffer = |buffer: String| {
-        if buffer.len() == 1 {
+        if full_buffer.len() != 1 {
             full_buffer.push_str(", ");
         }
         full_buffer.push('"');