diff --git a/helper/schema/schema.go b/helper/schema/schema.go
index 69c12759c..11906e373 100644
--- a/helper/schema/schema.go
+++ b/helper/schema/schema.go
@@ -178,14 +178,15 @@ func (m schemaMap) InternalValidate() error {
 			return fmt.Errorf("%s: ComputedWhen can only be set with Computed", k)
 		}
 
-		if v.Type == TypeList {
+		if v.Type == TypeList || v.Type == TypeSet {
 			if v.Elem == nil {
 				return fmt.Errorf("%s: Elem must be set for lists", k)
 			}
 
-			// TODO: test
-			if v.Set != nil {
+			if v.Type == TypeList && v.Set != nil {
 				return fmt.Errorf("%s: Set can only be set for TypeSet", k)
+			} else if v.Type == TypeSet && v.Set == nil {
+				return fmt.Errorf("%s: Set must be set", k)
 			}
 
 			switch t := v.Elem.(type) {
diff --git a/helper/schema/schema_test.go b/helper/schema/schema_test.go
index 36ca3bb54..ee06514fe 100644
--- a/helper/schema/schema_test.go
+++ b/helper/schema/schema_test.go
@@ -784,6 +784,29 @@ func TestSchemaMap_InternalValidate(t *testing.T) {
 			true,
 		},
 
+		// List element with Set set
+		{
+			map[string]*Schema{
+				"foo": &Schema{
+					Type: TypeList,
+					Elem: &Schema{Type: TypeInt},
+					Set:  func(interface{}) int { return 0 },
+				},
+			},
+			true,
+		},
+
+		// Set element with no Set set
+		{
+			map[string]*Schema{
+				"foo": &Schema{
+					Type: TypeSet,
+					Elem: &Schema{Type: TypeInt},
+				},
+			},
+			true,
+		},
+
 		// Required but computed
 		{
 			map[string]*Schema{