diff --git a/cache.go b/cache.go
index 55af84a..83ca900 100644
--- a/cache.go
+++ b/cache.go
@@ -32,16 +32,6 @@ func (item Item) Expired() bool {
 	return item.Expiration != 0 && time.Now().UnixNano() > item.Expiration
 }
 
-const (
-	// NoExpiration is for use with functions that take no expiration time.
-	NoExpiration time.Duration = -1
-	// DefaultExpiration is for use with functions that take an
-	// expiration time. Equivalent to passing in the same expiration
-	// duration as was given to New() when the cache was
-	// created (e.g. 5 minutes.)
-	DefaultExpiration time.Duration = 0
-)
-
 // Cache struct
 type Cache_tpl struct {
 	*cache
diff --git a/cachemap/cache.tmpl b/cachemap/cache.tmpl
index 1e10eaa..a7ec550 100644
--- a/cachemap/cache.tmpl
+++ b/cachemap/cache.tmpl
@@ -32,16 +32,6 @@ func (item Item) Expired() bool {
 	return item.Expiration != 0 && time.Now().UnixNano() > item.Expiration
 }
 
-const (
-	// NoExpiration is for use with functions that take no expiration time.
-	NoExpiration time.Duration = -1
-	// DefaultExpiration is for use with functions that take an
-	// expiration time. Equivalent to passing in the same expiration
-	// duration as was given to New() when the cache was
-	// created (e.g. 5 minutes.)
-	DefaultExpiration time.Duration = 0
-)
-
 // Cache struct
 type {{.ValueType}}Cache struct {
 	*cache
diff --git a/cachemap/const.tmpl b/cachemap/const.tmpl
new file mode 100644
index 0000000..8b61a4a
--- /dev/null
+++ b/cachemap/const.tmpl
@@ -0,0 +1,19 @@
+package {{.PackageName}}
+
+import (
+	"time"
+)
+
+// To avoid redecleration, put common code in this file.
+
+const (
+	// NoExpiration is for use with functions that take no expiration time.
+	NoExpiration time.Duration = -1
+	// DefaultExpiration is for use with functions that take an
+	// expiration time. Equivalent to passing in the same expiration
+	// duration as was given to New() when the cache was
+	// created (e.g. 5 minutes.)
+	DefaultExpiration time.Duration = 0
+)
+
+
diff --git a/cachemap/main.go b/cachemap/main.go
index deab2ba..18b4ddf 100644
--- a/cachemap/main.go
+++ b/cachemap/main.go
@@ -157,7 +157,7 @@ FIND:
 	if err != nil {
 		fatal(err)
 	}
-	if isBuiltin(*valueType) {
+	if !isBuiltin(*valueType) {
 		*valueType = strings.Title(*valueType)
 	}
 	err = tpl.Execute(
@@ -174,4 +174,20 @@ FIND:
 	if err != nil {
 		fatal(err)
 	}
+	constFile, err := os.OpenFile(fmt.Sprintf("cachemap_const.go"), os.O_TRUNC|os.O_WRONLY|os.O_CREATE, 0644)
+	if err != nil {
+		fatal(err)
+	}
+	defer constFile.Close()
+	constTpl, err := template.New("const.tmpl").ParseFiles(filepath.Join(packageDir(), "const.tmpl"))
+	if err != nil {
+		fatal(err)
+	}
+	err = constTpl.Execute(constFile,
+		map[string]interface{}{
+			"PackageName": packageName,
+		})
+	if err != nil {
+		fatal(err)
+	}
 }
diff --git a/const.go b/const.go
new file mode 100644
index 0000000..22b8518
--- /dev/null
+++ b/const.go
@@ -0,0 +1,17 @@
+package cache
+
+import (
+	"time"
+)
+
+// To avoid redecleration errors, put common code in this file.
+
+const (
+	// NoExpiration is for use with functions that take no expiration time.
+	NoExpiration time.Duration = -1
+	// DefaultExpiration is for use with functions that take an
+	// expiration time. Equivalent to passing in the same expiration
+	// duration as was given to New() when the cache was
+	// created (e.g. 5 minutes.)
+	DefaultExpiration time.Duration = 0
+)