diff --git a/core/fpdfapi/parser/cpdf_syntax_parser.h b/core/fpdfapi/parser/cpdf_syntax_parser.h
index f8425f6..b7bcecd 100644
--- a/core/fpdfapi/parser/cpdf_syntax_parser.h
+++ b/core/fpdfapi/parser/cpdf_syntax_parser.h
@@ -29,7 +29,7 @@
 
 class CPDF_SyntaxParser {
  public:
-  enum class ParseType { kStrict, kLoose };
+  enum class ParseType : bool { kStrict, kLoose };
 
   struct WordResult {
     ByteString word;