diff --git a/share/functions/__fish_config_interactive.fish b/share/functions/__fish_config_interactive.fish
index 0b0ba7e47..e2164f00d 100644
--- a/share/functions/__fish_config_interactive.fish
+++ b/share/functions/__fish_config_interactive.fish
@@ -36,6 +36,11 @@ function __fish_config_interactive -d "Initializations that should be performed
         set -U fish_greeting "$line1$line2"
     end
 
+    if set -q fish_private_mode
+        set -l line (_ "fish is running in private mode, history will not be persisted.")
+        set -g fish_greeting $fish_greeting.\n$line
+    end
+
     #
     # If we are starting up for the first time, set various defaults.
     #
diff --git a/src/env.cpp b/src/env.cpp
index 84a229636..ba7627dc7 100644
--- a/src/env.cpp
+++ b/src/env.cpp
@@ -296,7 +296,8 @@ bool string_set_contains(const T &set, const wchar_t *val) {
 
 /// Check if a variable may not be set using the set command.
 static bool is_read_only(const wchar_t *val) {
-    const string_set_t env_read_only = {L"PWD", L"SHLVL", L"history", L"status", L"version", L"fish_pid", L"hostname", L"_"};
+    const string_set_t env_read_only = {L"PWD", L"SHLVL", L"history", L"status", L"version",
+        L"fish_pid", L"hostname", L"_", L"fish_private_mode"};
     return string_set_contains(env_read_only, val) ||
         (in_private_mode() && wcscmp(L"fish_history", val) == 0);
 }
diff --git a/src/history.cpp b/src/history.cpp
index 81240feab..d96ffefdc 100644
--- a/src/history.cpp
+++ b/src/history.cpp
@@ -1992,6 +1992,7 @@ static bool private_mode = false;
 void start_private_mode() {
     private_mode = true;
     env_set_one(L"fish_history", ENV_GLOBAL, L"");
+    env_set_one(L"fish_private_mode", ENV_GLOBAL, L"1");
 }
 
 bool in_private_mode() {