diff --git a/ext/gpgme/extconf.rb b/ext/gpgme/extconf.rb
index c0cea4f..7dd4dc6 100644
--- a/ext/gpgme/extconf.rb
+++ b/ext/gpgme/extconf.rb
@@ -126,7 +126,7 @@
       '--disable-g13-test',
       # We only need the C API.
       '--disable-languages',
-      "CFLAGS=-fPIC #{ENV["CFLAGS"]}",
+      "CFLAGS=-D_LARGEFILE64_SOURCE -fPIC #{ENV["CFLAGS"]}",
     ]
     checkpoint = "#{recipe.target}/#{recipe.name}-#{recipe.version}-#{recipe.host}.installed"
     unless File.exist?(checkpoint)