diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index cfb34d7eb8..e080d8cc5a 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -243,6 +243,13 @@ static void initAndRun(int argc, char * * argv)
             maxSilentTime = getIntArg(arg, i, args.end());
         else if (arg == "--no-build-hook")
             useBuildHook = false;
+        else if (arg == "--option") {
+            ++i; if (i == args.end()) throw UsageError("`--option' requires two arguments");
+            string name = *i;
+            ++i; if (i == args.end()) throw UsageError("`--option' requires two arguments");
+            string value = *i;
+            overrideSetting(name, tokenizeString(value));
+        }
         else remaining.push_back(arg);
     }
 
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index 296cc4ac80..907627b659 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -34,6 +34,9 @@ static bool settingsRead = false;
 
 static std::map<string, Strings> settings;
 
+/* Overriden settings. */
+std::map<string, Strings> settingsCmdline;
+
 
 string & at(Strings & ss, unsigned int n)
 {
@@ -73,6 +76,8 @@ static void readSettings()
         advance(i, 2);
         settings[name] = Strings(i, tokens.end());
     };
+
+    settings.insert(settingsCmdline.begin(), settingsCmdline.end());
     
     settingsRead = true;
 }
@@ -118,6 +123,13 @@ unsigned int queryIntSetting(const string & name, unsigned int def)
 }
 
 
+void overrideSetting(const string & name, const Strings & value)
+{
+    if (settingsRead) settings[name] = value;
+    settingsCmdline[name] = value;
+}
+
+
 void reloadSettings()
 {
     settingsRead = false;
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index b8e2bae66e..687247cc74 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -101,6 +101,8 @@ bool queryBoolSetting(const string & name, bool def);
 
 unsigned int queryIntSetting(const string & name, unsigned int def);
 
+void overrideSetting(const string & name, const Strings & value);
+
 void reloadSettings();