diff --git a/core/fpdfapi/font/cpdf_tounicodemap.cpp b/core/fpdfapi/font/cpdf_tounicodemap.cpp
index 348cdb8..d1df1f8 100644
--- a/core/fpdfapi/font/cpdf_tounicodemap.cpp
+++ b/core/fpdfapi/font/cpdf_tounicodemap.cpp
@@ -136,7 +136,7 @@
     else if (word == "/Adobe-GB1-UCS2")
       cid_set = CIDSET_GB1;
   }
-  if (cid_set) {
+  if (cid_set != CIDSET_UNKNOWN) {
     auto* manager = CPDF_FontGlobals::GetInstance()->GetCMapManager();
     m_pBaseMap = manager->GetCID2UnicodeMap(cid_set);
   }