diff --git a/src/optionstr.c b/src/optionstr.c
index 6cc4cf5..94a1e2a 100644
--- a/src/optionstr.c
+++ b/src/optionstr.c
@@ -454,6 +454,7 @@
     unblock_autocmds();
 }
 
+#if defined(FEAT_PROP_POPUP) || defined(PROTO)
 /*
  * Like set_string_option_direct(), but for a buffer-local option in "buf".
  * Blocks autocommands to avoid the old curbuf becoming invalid.
@@ -477,6 +478,7 @@
     curwin->w_buffer = curbuf;
     unblock_autocmds();
 }
+#endif
 
 /*
  * Set a string option to a new value, and handle the effects.