diff --git a/src/DecoderList.hxx b/src/DecoderList.hxx
index 2ca8eb794..50848ad4e 100644
--- a/src/DecoderList.hxx
+++ b/src/DecoderList.hxx
@@ -29,6 +29,7 @@ extern bool decoder_plugins_enabled[];
 
 /* interface for using plugins */
 
+gcc_pure
 const struct DecoderPlugin *
 decoder_plugin_from_name(const char *name);