diff --git a/resources/celerity/map.php b/resources/celerity/map.php
--- a/resources/celerity/map.php
+++ b/resources/celerity/map.php
@@ -397,7 +397,7 @@
     'rsrc/js/application/herald/PathTypeahead.js' => 'ad486db3',
     'rsrc/js/application/herald/herald-rule-editor.js' => '0922e81d',
     'rsrc/js/application/maniphest/behavior-batch-selector.js' => '139ef688',
-    'rsrc/js/application/maniphest/behavior-line-chart.js' => '11167911',
+    'rsrc/js/application/maniphest/behavior-line-chart.js' => '495cf14d',
     'rsrc/js/application/maniphest/behavior-list-edit.js' => 'c687e867',
     'rsrc/js/application/owners/OwnersPathEditor.js' => '2a8b62d9',
     'rsrc/js/application/owners/owners-path-editor.js' => 'ff688a7a',
@@ -625,7 +625,7 @@
     'javelin-behavior-icon-composer' => '38a6cedb',
     'javelin-behavior-launch-icon-composer' => 'a17b84f1',
     'javelin-behavior-lightbox-attachments' => 'c7e748bf',
-    'javelin-behavior-line-chart' => '11167911',
+    'javelin-behavior-line-chart' => '495cf14d',
     'javelin-behavior-linked-container' => '74446546',
     'javelin-behavior-maniphest-batch-selector' => '139ef688',
     'javelin-behavior-maniphest-list-editor' => 'c687e867',
@@ -1007,12 +1007,6 @@
       'javelin-workflow',
       'phuix-icon-view',
     ),
-    11167911 => array(
-      'javelin-behavior',
-      'javelin-dom',
-      'javelin-vector',
-      'phui-chart-css',
-    ),
     '111bfd2d' => array(
       'javelin-install',
     ),
@@ -1325,6 +1319,12 @@
     '490e2e2e' => array(
       'phui-oi-list-view-css',
     ),
+    '495cf14d' => array(
+      'javelin-behavior',
+      'javelin-dom',
+      'javelin-vector',
+      'phui-chart-css',
+    ),
     '4a7fb02b' => array(
       'javelin-behavior',
       'javelin-dom',
diff --git a/src/applications/fact/controller/PhabricatorFactChartController.php b/src/applications/fact/controller/PhabricatorFactChartController.php
--- a/src/applications/fact/controller/PhabricatorFactChartController.php
+++ b/src/applications/fact/controller/PhabricatorFactChartController.php
@@ -55,8 +55,29 @@
       }
     }
 
-    $x = array_keys($points);
-    $y = array_values($points);
+    $datasets = array();
+
+    $datasets[] = array(
+      'x' => array_keys($points),
+      'y' => array_values($points),
+      'color' => '#ff0000',
+    );
+
+
+    // Add a dummy "y = x" dataset to prove we can draw multiple datasets.
+    $x_min = min(array_keys($points));
+    $x_max = max(array_keys($points));
+    $x_range = ($x_max - $x_min) / 4;
+    $linear = array();
+    foreach ($points as $x => $y) {
+      $linear[$x] = count($points) * (($x - $x_min) / $x_range);
+    }
+    $datasets[] = array(
+      'x' => array_keys($linear),
+      'y' => array_values($linear),
+      'color' => '#0000ff',
+    );
+
 
     $id = celerity_generate_unique_node_id();
     $chart = phutil_tag(
@@ -70,15 +91,38 @@
 
     require_celerity_resource('d3');
 
-    Javelin::initBehavior('line-chart', array(
-      'hardpoint' => $id,
-      'x' => array($x),
-      'y' => array($y),
-      'yMax' => max(0, max($y)),
-      'yMin' => min(0, min($y)),
-      'xformat' => 'epoch',
-      'colors' => array('#0000ff'),
-    ));
+    $y_min = 0;
+    $y_max = 0;
+    $x_min = null;
+    $x_max = 0;
+    foreach ($datasets as $dataset) {
+      if (!$dataset['y']) {
+        continue;
+      }
+
+      $y_min = min($y_min, min($dataset['y']));
+      $y_max = max($y_max, max($dataset['y']));
+
+      if ($x_min === null) {
+        $x_min = min($dataset['x']);
+      } else {
+        $x_min = min($x_min, min($dataset['x']));
+      }
+
+      $x_max = max($x_max, max($dataset['x']));
+    }
+
+    Javelin::initBehavior(
+      'line-chart',
+      array(
+        'hardpoint' => $id,
+        'datasets' => $datasets,
+        'xMin' => $x_min,
+        'xMax' => $x_max,
+        'yMin' => $y_min,
+        'yMax' => $y_max,
+        'xformat' => 'epoch',
+      ));
 
     $box = id(new PHUIObjectBoxView())
       ->setHeaderText(pht('Count of %s', $fact->getName()))
diff --git a/webroot/rsrc/js/application/maniphest/behavior-line-chart.js b/webroot/rsrc/js/application/maniphest/behavior-line-chart.js
--- a/webroot/rsrc/js/application/maniphest/behavior-line-chart.js
+++ b/webroot/rsrc/js/application/maniphest/behavior-line-chart.js
@@ -57,28 +57,61 @@
       .attr('width', size.width)
       .attr('height', size.height);
 
-  var line = d3.svg.line()
-    .x(function(d) { return x(d.date); })
-    .y(function(d) { return y(d.count); });
-
-  var data = [];
-  for (var ii = 0; ii < config.x[0].length; ii++) {
-    data.push(
-      {
-        date: new Date(config.x[0][ii] * 1000),
-        count: +config.y[0][ii]
-      });
+  function as_date(value) {
+    return new Date(value * 1000);
   }
 
-  x.domain(d3.extent(data, function(d) { return d.date; }));
-
-  var yex = d3.extent(data, function(d) { return d.count; });
+  x.domain([as_date(config.xMin), as_date(config.xMax)]);
   y.domain([config.yMin, config.yMax]);
 
-  g.append('path')
-    .datum(data)
-    .attr('class', 'line')
-    .attr('d', line);
+  for (var idx = 0; idx < config.datasets.length; idx++) {
+    var dataset = config.datasets[idx];
+
+    var line = d3.svg.line()
+      .x(function(d) { return x(d.xvalue); })
+      .y(function(d) { return y(d.yvalue); });
+
+    var data = [];
+    for (var ii = 0; ii < dataset.x.length; ii++) {
+      data.push(
+        {
+          xvalue: as_date(dataset.x[ii]),
+          yvalue: dataset.y[ii]
+        });
+    }
+
+    g.append('path')
+      .datum(data)
+      .attr('class', 'line')
+      .style('stroke', dataset.color)
+      .attr('d', line);
+
+    g.selectAll('dot')
+      .data(data)
+      .enter()
+      .append('circle')
+      .attr('class', 'point')
+      .attr('r', 3)
+      .attr('cx', function(d) { return x(d.xvalue); })
+      .attr('cy', function(d) { return y(d.yvalue); })
+      .on('mouseover', function(d) {
+        var d_y = d.xvalue.getFullYear();
+
+        // NOTE: Javascript months are zero-based. See PHI1017.
+        var d_m = d.xvalue.getMonth() + 1;
+
+        var d_d = d.xvalue.getDate();
+
+        div
+          .html(d_y + '-' + d_m + '-' + d_d + ': ' + d.yvalue)
+          .style('opacity', 0.9)
+          .style('left', (d3.event.pageX - 60) + 'px')
+          .style('top', (d3.event.pageY - 38) + 'px');
+        })
+      .on('mouseout', function() {
+        div.style('opacity', 0);
+      });
+  }
 
   g.append('g')
     .attr('class', 'x axis')
@@ -95,30 +128,4 @@
     .attr('class', 'chart-tooltip')
     .style('opacity', 0);
 
-  g.selectAll('dot')
-    .data(data)
-    .enter()
-    .append('circle')
-    .attr('class', 'point')
-    .attr('r', 3)
-    .attr('cx', function(d) { return x(d.date); })
-    .attr('cy', function(d) { return y(d.count); })
-    .on('mouseover', function(d) {
-      var d_y = d.date.getFullYear();
-
-      // NOTE: Javascript months are zero-based. See PHI1017.
-      var d_m = d.date.getMonth() + 1;
-
-      var d_d = d.date.getDate();
-
-      div
-        .html(d_y + '-' + d_m + '-' + d_d + ': ' + d.count)
-        .style('opacity', 0.9)
-        .style('left', (d3.event.pageX - 60) + 'px')
-        .style('top', (d3.event.pageY - 38) + 'px');
-      })
-    .on('mouseout', function() {
-      div.style('opacity', 0);
-    });
-
 });