diff --git a/src/main.c b/src/main.c
index 13bdf5d3..07aa7774 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1315,6 +1315,9 @@ int DoDebug(ParsePtr p)
             if (val) DebugFlag |= DB_TRACE_FILES;
             else     DebugFlag &= ~DB_TRACE_FILES;
             break;
+        default:
+            Wprint(GetErr(M_BAD_DB_FLAG), ch);
+            break;
         }
     }
 }