diff --git a/lib/carto/tree/reference.js b/lib/carto/tree/reference.js
index a10fa8f..9c69d98 100644
--- a/lib/carto/tree/reference.js
+++ b/lib/carto/tree/reference.js
@@ -165,6 +165,9 @@ ref.validValue = function(env, selector, value) {
         return true;
     } else if (ref.selector(selector).type == 'tags') {
         if (!value.value) return false;
+        if (!value.value[0].value) {
+            return value.value[0].is === 'tag';
+        }
         for (i = 0; i < value.value[0].value.length; i++) {
             if (value.value[0].value[i].is !== 'tag') return false;
         }
diff --git a/test/rendering/raster_colorizer_onestop.mml b/test/rendering/raster_colorizer_onestop.mml
new file mode 100644
index 0000000..b99cdd7
--- /dev/null
+++ b/test/rendering/raster_colorizer_onestop.mml
@@ -0,0 +1,14 @@
+{
+    "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over",
+    "Stylesheet": [
+        "raster_colorizer_onestop.mss"
+    ],
+    "Layer": [{
+        "name": "world",
+        "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over",
+        "Datasource": {
+            "file": "http://tilemill-data.s3.amazonaws.com/test_data/shape_demo.zip",
+            "type": "shape"
+        }
+    }]
+}
diff --git a/test/rendering/raster_colorizer_onestop.mss b/test/rendering/raster_colorizer_onestop.mss
new file mode 100644
index 0000000..e8156ad
--- /dev/null
+++ b/test/rendering/raster_colorizer_onestop.mss
@@ -0,0 +1,7 @@
+#world {
+  raster-opacity:1;
+  raster-scaling:bilinear;
+  raster-colorizer-default-mode: linear;
+  raster-colorizer-default-color: transparent;
+  raster-colorizer-stops: stop(0,#000);
+}
diff --git a/test/rendering/raster_colorizer_onestop.result b/test/rendering/raster_colorizer_onestop.result
new file mode 100644
index 0000000..651c037
--- /dev/null
+++ b/test/rendering/raster_colorizer_onestop.result
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!DOCTYPE Map[]>
+<Map srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over" maximum-extent="-20037508.34,-20037508.34,20037508.34,20037508.34">
+
+
+<Style name="world" filter-mode="first">
+  <Rule>
+    <RasterSymbolizer opacity="1" scaling="bilinear" default-mode="linear" default-color="rgba(0, 0, 0, 0)" >
+	<stop value="0" color="#000000" /></RasterSymbolizer>
+  </Rule>
+</Style>
+<Layer name="world"
+  srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over">
+    <StyleName>world</StyleName>
+    <Datasource>
+       <Parameter name="file"><![CDATA[[absolute path]]]></Parameter>
+       <Parameter name="type"><![CDATA[shape]]></Parameter>
+    </Datasource>
+  </Layer>
+
+</Map>
diff --git a/test/rendering/transforms_single.mml b/test/rendering/transforms_single.mml
new file mode 100644
index 0000000..b3eae98
--- /dev/null
+++ b/test/rendering/transforms_single.mml
@@ -0,0 +1,14 @@
+{
+    "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over",
+    "Stylesheet": [
+        "transforms_single.mss"
+    ],
+    "Layer": [{
+        "name": "world",
+        "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over",
+        "Datasource": {
+            "file": "http://tilemill-data.s3.amazonaws.com/test_data/shape_demo.zip",
+            "type": "shape"
+        }
+    }]
+}
diff --git a/test/rendering/transforms_single.mss b/test/rendering/transforms_single.mss
new file mode 100644
index 0000000..6b4d81f
--- /dev/null
+++ b/test/rendering/transforms_single.mss
@@ -0,0 +1,3 @@
+#world {
+  point-transform: scale(2, 2);
+}
diff --git a/test/rendering/transforms_single.result b/test/rendering/transforms_single.result
new file mode 100644
index 0000000..0f8a790
--- /dev/null
+++ b/test/rendering/transforms_single.result
@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!DOCTYPE Map[]>
+<Map srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over" maximum-extent="-20037508.34,-20037508.34,20037508.34,20037508.34">
+
+
+<Style name="world" filter-mode="first">
+  <Rule>
+    <PointSymbolizer transform="scale(2,2)" />
+  </Rule>
+</Style>
+<Layer name="world"
+  srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over">
+    <StyleName>world</StyleName>
+    <Datasource>
+       <Parameter name="file"><![CDATA[[absolute path]]]></Parameter>
+       <Parameter name="type"><![CDATA[shape]]></Parameter>
+    </Datasource>
+  </Layer>
+
+</Map>