diff --git a/slicewriter.go b/slicewriter.go
index 9b10028..95ad63a 100644
--- a/slicewriter.go
+++ b/slicewriter.go
@@ -41,6 +41,8 @@ func (sw *SliceWriter) Write(w io.Writer, typ typewriter.Type) error {
 		return nil
 	}
 
+	tag.AddDefaultsIfNeeded(typ, templates[1:])
+
 	if includeSortImplementation(tag.Values) {
 		s := `// Sort implementation is a modification of http://golang.org/pkg/sort/#Sort
 // Copyright 2009 The Go Authors. All rights reserved.
@@ -120,6 +122,13 @@ func (sw *SliceWriter) Write(w io.Writer, typ typewriter.Type) error {
 }
 
 func includeSortImplementation(values []typewriter.TagValue) bool {
+	// Don't include it if it's already included.
+	for _, v := range values {
+		if v.Name == "sortImplementation" {
+			return false
+		}
+	}
+
 	for _, v := range values {
 		if strings.HasPrefix(v.Name, "SortBy") {
 			return true
@@ -129,6 +138,13 @@ func includeSortImplementation(values []typewriter.TagValue) bool {
 }
 
 func includeSortInterface(values []typewriter.TagValue) bool {
+	// Don't include it if it's already included.
+	for _, v := range values {
+		if v.Name == "sortInterface" {
+			return false
+		}
+	}
+
 	reg := regexp.MustCompile(`^Sort(Desc)?$`)
 	for _, v := range values {
 		if reg.MatchString(v.Name) {
diff --git a/sortimplementation.go b/sortimplementation.go
index 1b2bf77..fffb15e 100644
--- a/sortimplementation.go
+++ b/sortimplementation.go
@@ -177,4 +177,6 @@ func quickSort{{.SliceName}}(rcv {{.SliceName}}, less func({{.Type}}, {{.Type}})
 		insertionSort{{.SliceName}}(rcv, less, a, b)
 	}
 }
-`}
+`,
+	TypeConstraint: typewriter.Constraint{Ordered: true},
+}
diff --git a/sortinterface.go b/sortinterface.go
index a267df4..4f6f089 100644
--- a/sortinterface.go
+++ b/sortinterface.go
@@ -14,4 +14,6 @@ func (rcv {{.SliceName}}) Less(i, j int) bool {
 func (rcv {{.SliceName}}) Swap(i, j int) {
 	rcv[i], rcv[j] = rcv[j], rcv[i]
 }
-`}
+`,
+	TypeConstraint: typewriter.Constraint{Ordered: true},
+}