diff --git a/inlineOtherContent.go b/inlineOtherContent.go
index dec8bd2..d55bc8d 100644
--- a/inlineOtherContent.go
+++ b/inlineOtherContent.go
@@ -1,5 +1,7 @@
 package atomfeed
 
+import "errors"
+
 type InlineOtherContent struct {
 	*CommonAttributes
 	Type       MediaType `xml:"type,attr,omitempty"`
@@ -12,4 +14,10 @@ func (i *InlineOtherContent) hasSRC() bool { return false }
 
 func (i *InlineOtherContent) getType() string { return string(i.Type) }
 
-func (i *InlineOtherContent) Check() error { return nil }
+func (i *InlineOtherContent) Check() error {
+	if isCompositeMediaType(i.getType()) {
+		return errors.New("type attribute of inline other content must not be a composite type")
+	}
+
+	return nil
+}
diff --git a/outOfLineContent.go b/outOfLineContent.go
index e3805e9..17d4f64 100644
--- a/outOfLineContent.go
+++ b/outOfLineContent.go
@@ -15,6 +15,10 @@ func (o *OutOfLineContent) hasSRC() bool { return true }
 func (o *OutOfLineContent) getType() string { return string(o.Type) }
 
 func (o *OutOfLineContent) Check() error {
+	if isCompositeMediaType(o.getType()) {
+		return errors.New("type attribute of out of line content must not be a composite type")
+	}
+
 	if o.SRC == "" {
 		return errors.New("src attribute of out of line content empty")
 	}