diff --git a/m4/znc_visibility.m4 b/m4/znc_visibility.m4
index d47d529e..2c642eff 100644
--- a/m4/znc_visibility.m4
+++ b/m4/znc_visibility.m4
@@ -68,6 +68,7 @@ AC_DEFUN([ZNC_VISIBILITY],
          extern __attribute__((__visibility__("default"))) int exportedvar;
          extern __attribute__((__visibility__("hidden"))) int hiddenfunc (void);
          extern __attribute__((__visibility__("default"))) int exportedfunc (void);
+         void dummyfunc (void);
          void dummyfunc (void) {}]],
         [])],
         [znc_cv_cc_visibility=yes],