diff --git a/CMakeLists.txt b/CMakeLists.txt
index 261fa14..da4a788 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,6 +1,6 @@
 cmake_minimum_required (VERSION 3.2)
 project(libravatarserv
-        VERSION 0.5.0
+        VERSION 0.6.0
         LANGUAGES CXX
 )
 
diff --git a/README.md b/README.md
index 582a0bb..a7b034d 100644
--- a/README.md
+++ b/README.md
@@ -14,9 +14,11 @@ images tied to email or OpenID addresses.
 * Variable image size (`s` or `size`)
 * Default actions (`d` or `default`): 404, URL, mp/mm, identicon
 
-The default behaviour for unknown users is to return a 404 error. If a default
-image is put in the avatar directory, that is returned instead. The default
-image can not be overriden by adding the parameter `d` or `default` to the URL.
+The default behaviour for unknown users is to return a 404 error. You can change
+that by setting the environment variable `LIBRAVATARSERV_DEFAULT_FALLBACK` to
+any value accepted by `d` or `default`. If a default image is put in the avatar
+directory, that is returned instead. The default image can not be overridden by
+adding the parameter `d` or `default` to the URL.
 
 Clients are asked to cache results for up to 1 day to reduce load. This can
 apply to negative results as well.
@@ -50,7 +52,7 @@ HTTPS.
 
 libravatarserv looks in each of `${XDG_DATA_DIRS}` for a directory named
 `libravatarserv`. You can force a different directory by setting the environment
-variable `${LIBRAVATARSERV_DIR}` (until 0.3.0 `${AVATAR_DIR}`).
+variable `LIBRAVATARSERV_DIR` (until 0.3.0 `AVATAR_DIR`).
 
 The image files are named like your email address, no file extension. If you
 want to deliver a default image for unknown email addresses, name it `default`.
diff --git a/doc/nginx-example.conf b/doc/nginx-example.conf
index 4da88bf..9044b54 100644
--- a/doc/nginx-example.conf
+++ b/doc/nginx-example.conf
@@ -13,6 +13,7 @@ server {
         include /etc/nginx/fastcgi_params;
         fastcgi_pass    unix:/var/run/cgi-fcgiwrap.socket-1;
         fastcgi_param SCRIPT_FILENAME /usr/bin/libravatarserv;
+        fastcgi_param LIBRAVATARSERV_DEFAULT_FALLBACK 404;
     }
 }
 
@@ -28,5 +29,6 @@ server {
         include /etc/nginx/fastcgi_params;
         fastcgi_pass    unix:/var/run/cgi-fcgiwrap.socket-1;
         fastcgi_param SCRIPT_FILENAME /usr/bin/libravatarserv;
+        fastcgi_param LIBRAVATARSERV_DEFAULT_FALLBACK 404;
     }
 }
diff --git a/src/libravatarserv.cpp b/src/libravatarserv.cpp
index 3863e15..afdb9f6 100644
--- a/src/libravatarserv.cpp
+++ b/src/libravatarserv.cpp
@@ -24,10 +24,12 @@ using std::cout;
 using std::cerr;
 using std::endl;
 using global::avatar_dir;
+using global::settings;
 
 // Global variables
 std::map<const string, const string> hash::table;
 fs::path global::avatar_dir = "";
+global::Settings global::settings;
 
 
 int main()
@@ -51,6 +53,7 @@ int main()
         return 3;
     }
     hash::fill_table();
+    read_settings();
 
     http::Request avatar = http::parse_request(request);
 
@@ -62,6 +65,10 @@ int main()
     else
     {
         cerr << "Error " << std::to_string(image.error) << ": Could not open file.\n";
+        if (avatar.fallback.empty())
+        {
+            avatar.fallback = settings.default_fallback;
+        }
         if (avatar.fallback.substr(0, 4) == "http")
         {
             cout << "Status: 307 Temporary Redirect\n";
@@ -145,3 +152,12 @@ bool find_avatar_dir()
 
     return true;
 }
+
+void read_settings()
+{
+    const char *env = std::getenv("LIBRAVATARSERV_DEFAULT_FALLBACK");
+    if (env != nullptr)
+    {
+        global::settings.default_fallback = env;
+    }
+}
diff --git a/src/libravatarserv.hpp b/src/libravatarserv.hpp
index ced0036..63451a9 100644
--- a/src/libravatarserv.hpp
+++ b/src/libravatarserv.hpp
@@ -37,10 +37,15 @@ using std::uint8_t;
 
 int main();
 bool find_avatar_dir();
+void read_settings();
 
 namespace global
 {
     extern fs::path avatar_dir;
+    extern struct Settings
+    {
+        string default_fallback;
+    } settings;
 }
 
 namespace http  // http.cpp
@@ -49,7 +54,7 @@ namespace http  // http.cpp
     {
         const string digest;
         const uint16_t size;
-        const string fallback;
+        string fallback;
     };
 
     const Request parse_request(const string &request);