diff --git a/src/history.cpp b/src/history.cpp
index 931d614ca..583968130 100644
--- a/src/history.cpp
+++ b/src/history.cpp
@@ -1584,11 +1584,6 @@ std::shared_ptr<history_t> history_t::with_name(const wcstring &name) {
     return hist;
 }
 
-void start_private_mode(env_stack_t &vars) {
-    vars.set_one(L"fish_history", ENV_GLOBAL, L"");
-    vars.set_one(L"fish_private_mode", ENV_GLOBAL, L"1");
-}
-
 bool in_private_mode(const environment_t &vars) {
     return vars.get_unless_empty(L"fish_private_mode").has_value();
 }
diff --git a/src/history.h b/src/history.h
index 1d6d49d54..fc029509b 100644
--- a/src/history.h
+++ b/src/history.h
@@ -342,9 +342,6 @@ path_list_t expand_and_detect_paths(const path_list_t &paths, const environment_
 */
 bool all_paths_are_valid(const path_list_t &paths, const operation_context_t &ctx);
 
-/** Sets private mode on. Once in private mode, it cannot be turned off. */
-void start_private_mode(env_stack_t &vars);
-
 /** Queries private mode status. */
 bool in_private_mode(const environment_t &vars);