diff --git a/media/mediaType.go b/media/mediaType.go
index 18af666d59a..819de9d8028 100644
--- a/media/mediaType.go
+++ b/media/mediaType.go
@@ -274,6 +274,8 @@ var DefaultTypes = Types{
 	YAMLType,
 	TOMLType,
 	PNGType,
+	GIFType,
+	BMPType,
 	JPEGType,
 	WEBPType,
 	AVIType,
@@ -289,6 +291,15 @@ var DefaultTypes = Types{
 
 func init() {
 	sort.Sort(DefaultTypes)
+
+	// Sanity check.
+	seen := make(map[Type]bool)
+	for _, t := range DefaultTypes {
+		if seen[t] {
+			panic(fmt.Sprintf("MediaType %s duplicated in list", t))
+		}
+		seen[t] = true
+	}
 }
 
 // Types is a slice of media types.
diff --git a/media/mediaType_test.go b/media/mediaType_test.go
index 8c739813d79..cd4439fe79b 100644
--- a/media/mediaType_test.go
+++ b/media/mediaType_test.go
@@ -15,6 +15,7 @@ package media
 
 import (
 	"encoding/json"
+	"fmt"
 	"io/ioutil"
 	"path/filepath"
 	"sort"
@@ -63,7 +64,7 @@ func TestDefaultTypes(t *testing.T) {
 
 	}
 
-	c.Assert(len(DefaultTypes), qt.Equals, 31)
+	c.Assert(len(DefaultTypes), qt.Equals, 33)
 }
 
 func TestGetByType(t *testing.T) {
@@ -193,6 +194,7 @@ func TestFromContent(t *testing.T) {
 			content, err := ioutil.ReadFile(filename)
 			c.Assert(err, qt.IsNil)
 			ext := strings.TrimPrefix(paths.Ext(filename), ".")
+			fmt.Println("=>", ext)
 			expected, _, found := mtypes.GetFirstBySuffix(ext)
 			c.Assert(found, qt.IsTrue)
 			got := FromContent(mtypes, ext, content)
diff --git a/media/testdata/resource.bmp b/media/testdata/resource.bmp
new file mode 100644
index 00000000000..19759b33d22
Binary files /dev/null and b/media/testdata/resource.bmp differ
diff --git a/media/testdata/resource.gif b/media/testdata/resource.gif
new file mode 100644
index 00000000000..9549c0b9d3f
Binary files /dev/null and b/media/testdata/resource.gif differ