diff --git a/sqlite_utils/db.py b/sqlite_utils/db.py
index ff2957d..f698b7b 100644
--- a/sqlite_utils/db.py
+++ b/sqlite_utils/db.py
@@ -710,7 +710,7 @@ class Database:
         if str(value).upper() in ("CURRENT_TIME", "CURRENT_DATE", "CURRENT_TIMESTAMP"):
             return value
 
-        if str(value).upper() in ("TRUE", "FALSE", "NULL"):
+        if isinstance(value, str) and value.upper() in ("TRUE", "FALSE", "NULL"):
             # Keyword literals must stay unquoted; quoting them would turn the
             # default into a string ('TRUE' instead of 1, 'NULL' instead of null).
             return value