diff --git a/doc/manual/nix-collect-garbage.xml b/doc/manual/nix-collect-garbage.xml
index a13e365a4..a97e3b7c6 100644
--- a/doc/manual/nix-collect-garbage.xml
+++ b/doc/manual/nix-collect-garbage.xml
@@ -20,6 +20,7 @@
     <command>nix-collect-garbage</command>
     <arg><option>--delete-old</option></arg>
     <arg><option>-d</option></arg>
+    <arg><option>--delete-older-than</option> <replaceable>period</replaceable></arg>
     <group choice='opt'>
       <arg choice='plain'><option>--print-roots</option></arg>
       <arg choice='plain'><option>--print-live</option></arg>
@@ -35,13 +36,18 @@
 <para>The command <command>nix-collect-garbage</command> is mostly an
 alias of <link linkend="rsec-nix-store-gc"><command>nix-store
 --gc</command></link>, that is, it deletes all unreachable paths in
-the Nix store to clean up your system.  However, it provides an
-additional option <option>-d</option> (<option>--delete-old</option>)
-that deletes all old generations of all profiles in
+the Nix store to clean up your system.  However, it provides two
+additional options: <option>-d</option> (<option>--delete-old</option>),
+which deletes all old generations of all profiles in
 <filename>/nix/var/nix/profiles</filename> by invoking
-<literal>nix-env --delete-generations old</literal> on all profiles.
-Of course, this makes rollbacks to previous configurations
-impossible.</para>
+<literal>nix-env --delete-generations old</literal> on all profiles
+(of course, this makes rollbacks to previous configurations
+impossible); and
+<option>--delete-older-than</option> <replaceable>period</replaceable>,
+where period is a value such as <literal>30d</literal>, which deletes
+all non-current generations that are older than the specified number of
+days in all profiles in <filename>/nix/var/nix/profiles</filename>.
+</para>
 
 </refsection>
 
diff --git a/scripts/nix-collect-garbage.in b/scripts/nix-collect-garbage.in
index 28b0c749f..55e0ba7a6 100755
--- a/scripts/nix-collect-garbage.in
+++ b/scripts/nix-collect-garbage.in
@@ -8,12 +8,19 @@ my $profilesDir = "@localstatedir@/nix/profiles";
 
 # Process the command line arguments.
 my @args = ();
+my $arg;
+
 my $removeOld = 0;
+my $gen;
 my $dryRun = 0;
 
-for my $arg (@ARGV) {
+while ($arg = shift) {
     if ($arg eq "--delete-old" || $arg eq "-d") {
         $removeOld = 1;
+        $gen = "old";
+    } elsif ($arg eq "--delete-older-than") {
+        $removeOld = 1;
+        $gen = shift;
     } elsif ($arg eq "--dry-run") {
         $dryRun = 1;
     } elsif ($arg eq "--help") {
@@ -40,7 +47,8 @@ sub removeOldGenerations {
         $name = $dir . "/" . $name;
         if (-l $name && (readlink($name) =~ /link/)) {
             print STDERR "removing old generations of profile $name\n";
-            system("$Nix::Config::binDir/nix-env", "-p", $name, "--delete-generations", "old", $dryRun ? "--dry-run" : ());
+
+            system("$Nix::Config::binDir/nix-env", "-p", $name, "--delete-generations", $gen, $dryRun ? "--dry-run" : ());
         }
         elsif (! -l $name && -d $name) {
             removeOldGenerations $name;