diff --git a/src/proto/misc1.pro b/src/proto/misc1.pro
index cc7e07a..167805b 100644
--- a/src/proto/misc1.pro
+++ b/src/proto/misc1.pro
@@ -32,6 +32,7 @@
 void expand_env_esc(char_u *srcp, char_u *dst, int dstlen, int esc, int one, char_u *startstr);
 char_u *vim_getenv(char_u *name, int *mustfree);
 void vim_unsetenv(char_u *var);
+void vim_unsetenv_ext(char_u *var);
 void vim_setenv_ext(char_u *name, char_u *val);
 void vim_setenv(char_u *name, char_u *val);
 char_u *get_env_name(expand_T *xp, int idx);