diff --git a/src/tz.cpp b/src/tz.cpp
index 15c9f5db..a2ada66c 100644
--- a/src/tz.cpp
+++ b/src/tz.cpp
@@ -372,6 +372,7 @@ class file_streambuf
     virtual
     int_type
     underflow()
+    override
     {
         if (gptr() == egptr() && file_)
         {