diff --git a/src/lib/Hydra/Controller/Jobset.pm b/src/lib/Hydra/Controller/Jobset.pm
index 35b29d86..fb82a584 100644
--- a/src/lib/Hydra/Controller/Jobset.pm
+++ b/src/lib/Hydra/Controller/Jobset.pm
@@ -173,10 +173,16 @@ sub nixExprPathFromParams {
 
 
 sub checkInputValue {
-    my ($c, $type, $value) = @_;
+    my ($c, $name, $type, $value) = @_;
     $value = trim $value;
-    error($c, "Invalid Boolean value ‘$value’.") if
+    error($c, "The value ‘$value’ of input ‘$name’ is not a Boolean (‘true’ or ‘false’).") if
         $type eq "boolean" && !($value eq "true" || $value eq "false");
+    error($c, "The value ‘$value’ of input ‘$name’ does not specify a Hydra evaluation.  "
+          . "It should be either the number of a specific evaluation, the name of "
+          . "a jobset (given as <project>:<jobset>), or the name of a job (<project>:<jobset>:<job>).")
+        if $type eq "eval" && $value !~ /^\d+$/
+            && $value !~ /^$projectNameRE:$jobsetNameRE$/
+            && $value !~ /^$projectNameRE:$jobsetNameRE:$jobNameRE$/;
     return $value;
 }
 
@@ -237,7 +243,7 @@ sub updateJobset {
         my @values = ref($values) eq 'ARRAY' ? @{$values} : ($values);
         my $altnr = 0;
         foreach my $value (@values) {
-            $value = checkInputValue($c, $type, $value);
+            $value = checkInputValue($c, $name, $type, $value);
             $input->jobsetinputalts->create({altnr => $altnr++, value => $value});
         }
     }
@@ -294,7 +300,7 @@ sub evals_GET {
 # Redirect to the latest finished evaluation of this jobset.
 sub latest_eval : Chained('jobsetChain') PathPart('latest-eval') {
     my ($self, $c, @args) = @_;
-    my $eval = getLatestFinishedEval($c, $c->stash->{jobset})
+    my $eval = getLatestFinishedEval($c->stash->{jobset})
         or notFound($c, "No evaluation found.");
     $c->res->redirect($c->uri_for($c->controller('JobsetEval')->action_for("view"), [$eval->id], @args, $c->req->params));
 }
diff --git a/src/lib/Hydra/Controller/JobsetEval.pm b/src/lib/Hydra/Controller/JobsetEval.pm
index 74ab3bce..a2d8187c 100644
--- a/src/lib/Hydra/Controller/JobsetEval.pm
+++ b/src/lib/Hydra/Controller/JobsetEval.pm
@@ -47,7 +47,7 @@ sub view : Chained('eval') PathPart('') Args(0) {
         } elsif (defined $compare && $compare =~ /^($jobsetNameRE)$/) {
             my $j = $c->stash->{project}->jobsets->find({name => $compare})
                 or notFound($c, "Jobset $compare doesn't exist.");
-            $eval2 = getLatestFinishedEval($c, $j);
+            $eval2 = getLatestFinishedEval($j);
         } else {
             notFound($c, "Unknown comparison source ‘$compare’.");
         }
diff --git a/src/lib/Hydra/Controller/Root.pm b/src/lib/Hydra/Controller/Root.pm
index ad34ae40..0d7660a0 100644
--- a/src/lib/Hydra/Controller/Root.pm
+++ b/src/lib/Hydra/Controller/Root.pm
@@ -37,7 +37,8 @@ sub begin :Private {
         'boolean' => 'Boolean',
         'nix' => 'Nix expression',
         'build' => 'Build output',
-        'sysbuild' => 'Build output (same system)'
+        'sysbuild' => 'Build output (same system)',
+        'eval' => 'Previous Hydra evaluation'
     };
     $_->supportedInputTypes($c->stash->{inputTypes}) foreach @{$c->hydra_plugins};
 
diff --git a/src/lib/Hydra/Helper/AddBuilds.pm b/src/lib/Hydra/Helper/AddBuilds.pm
index a7e5c9c8..9e432473 100644
--- a/src/lib/Hydra/Helper/AddBuilds.pm
+++ b/src/lib/Hydra/Helper/AddBuilds.pm
@@ -17,6 +17,7 @@ use File::Temp;
 use File::Spec;
 use File::Slurp;
 use Hydra::Helper::PluginHooks;
+use Hydra::Helper::CatalystUtils;
 
 our @ISA = qw(Exporter);
 our @EXPORT = qw(
@@ -147,6 +148,51 @@ sub fetchInputSystemBuild {
     return @inputs;
 }
 
+
+sub fetchInputEval {
+    my ($db, $project, $jobset, $name, $value) = @_;
+
+    my $eval;
+
+    if ($value =~ /^\d+$/) {
+        $eval = $db->resultset('JobsetEvals')->find({ id => int($value) });
+        die "evaluation $eval->{id} does not exist\n" unless defined $eval;
+    } elsif ($value =~ /^($projectNameRE):($jobsetNameRE)$/) {
+        my $jobset = $db->resultset('Jobsets')->find({ project => $1, name => $2 });
+        die "jobset ‘$value’ does not exist\n" unless defined $jobset;
+        $eval = getLatestFinishedEval($jobset);
+        die "jobset ‘$value’ does not have a finished evaluation\n" unless defined $eval;
+    } elsif ($value =~ /^($projectNameRE):($jobsetNameRE):($jobNameRE)$/) {
+        $eval = $db->resultset('JobsetEvals')->find(
+            { project => $1, jobset => $2, hasnewbuilds => 1 },
+            { order_by => "id DESC", rows => 1
+            , where =>
+                \ [ # All builds in this jobset should be finished...
+                    "not exists (select 1 from JobsetEvalMembers m join Builds b on m.build = b.id where m.eval = me.id and b.finished = 0) "
+                    # ...and the specified build must have succeeded.
+                    . "and exists (select 1 from JobsetEvalMembers m join Builds b on m.build = b.id where m.eval = me.id and b.job = ? and b.buildstatus = 0)"
+                  , [ 'name', $3 ] ]
+            });
+        die "there is no successful build of ‘$value’ in a finished evaluation\n" unless defined $eval;
+    } else {
+        die;
+    }
+
+    my $jobs = {};
+    foreach my $build ($eval->builds) {
+        next unless $build->finished == 1 && $build->buildstatus == 0;
+        # FIXME: Handle multiple outputs.
+        my $out = $build->buildoutputs->find({ name => "out" });
+        next unless defined $out;
+        # FIXME: Should we fail if the path is not valid?
+        next unless isValidPath($out->path);
+        $jobs->{$build->get_column('job')} = $out->path;
+    }
+
+    return { jobs => $jobs };
+}
+
+
 sub fetchInput {
     my ($plugins, $db, $project, $jobset, $name, $type, $value, $emailresponsible) = @_;
     my @inputs;
@@ -157,6 +203,9 @@ sub fetchInput {
     elsif ($type eq "sysbuild") {
         @inputs = fetchInputSystemBuild($db, $project, $jobset, $name, $value);
     }
+    elsif ($type eq "eval") {
+        @inputs = fetchInputEval($db, $project, $jobset, $name, $value);
+    }
     elsif ($type eq "string" || $type eq "nix") {
         die unless defined $value;
         @inputs = { value => $value };
@@ -245,8 +294,18 @@ sub inputsToArgs {
                     push @res, "--arg", $input, booleanToString($exprType, $alt->{value});
                 }
                 when ("nix") {
+                    die "input type ‘nix’ only supported for Nix-based jobsets\n" unless $exprType eq "nix";
                     push @res, "--arg", $input, $alt->{value};
                 }
+                when ("eval") {
+                    die "input type ‘eval’ only supported for Nix-based jobsets\n" unless $exprType eq "nix";
+                    my $s = "{ ";
+                    # FIXME: escape $_.  But dots should not be escaped.
+                    $s .= "$_ = builtins.storePath ${\$alt->{jobs}->{$_}}; "
+                        foreach keys %{$alt->{jobs}};
+                    $s .= "}";
+                    push @res, "--arg", $input, $s;
+                }
                 default {
                     push @res, "--arg", $input, buildInputToString($exprType, $alt);
                 }
diff --git a/src/lib/Hydra/Helper/CatalystUtils.pm b/src/lib/Hydra/Helper/CatalystUtils.pm
index e83bd0ea..22fe3474 100644
--- a/src/lib/Hydra/Helper/CatalystUtils.pm
+++ b/src/lib/Hydra/Helper/CatalystUtils.pm
@@ -176,7 +176,7 @@ sub trim {
 
 
 sub getLatestFinishedEval {
-    my ($c, $jobset) = @_;
+    my ($jobset) = @_;
     my ($eval) = $jobset->jobsetevals->search(
         { hasnewbuilds => 1 },
         { order_by => "id DESC", rows => 1