diff --git a/api/tag/map.go b/api/tag/map.go
index 4bb537821b4d..7675c9738cb0 100644
--- a/api/tag/map.go
+++ b/api/tag/map.go
@@ -21,13 +21,15 @@ import (
 	"github.com/open-telemetry/opentelemetry-go/api/core"
 )
 
-type tagMap map[core.Key]tagContent
-
 type tagContent struct {
 	value core.Value
 	meta  core.MeasureMetadata
 }
 
+type tagMap map[core.Key]tagContent
+
+var _ Map = (*tagMap)(nil)
+
 func (t tagMap) Apply(a1 core.KeyValue, attributes []core.KeyValue, m1 core.Mutator, mutators []core.Mutator) Map {
 	m := make(tagMap, len(t)+len(attributes)+len(mutators))
 	for k, v := range t {
@@ -80,8 +82,6 @@ func (m tagMap) Foreach(f func(kv core.KeyValue) bool) {
 	}
 }
 
-var _ Map = (*tagMap)(nil)
-
 func (m tagMap) apply(mutator core.Mutator) {
 	if m == nil {
 		return
diff --git a/api/tag/tag.go b/api/tag/tag.go
index beef47829817..b586c123ff68 100644
--- a/api/tag/tag.go
+++ b/api/tag/tag.go
@@ -23,6 +23,12 @@ import (
 	"github.com/open-telemetry/opentelemetry-go/exporter/observer"
 )
 
+type ctxTagsType struct{}
+
+var (
+	ctxTagsKey = &ctxTagsType{}
+)
+
 type registeredKey struct {
 	name    string
 	desc    string
@@ -30,15 +36,7 @@ type registeredKey struct {
 	eventID core.EventID
 }
 
-type ctxTagsType struct{}
-
-type measure struct {
-	rk *registeredKey
-}
-
-var (
-	ctxTagsKey = &ctxTagsType{}
-)
+var _ core.Key = (*registeredKey)(nil)
 
 func register(name string, opts []Option) *registeredKey {
 	rk := &registeredKey{
@@ -195,6 +193,12 @@ func (k *registeredKey) Value(ctx context.Context) core.KeyValue {
 	}
 }
 
+type measure struct {
+	rk *registeredKey
+}
+
+var _ core.Mearsure = (*measure)(nil)
+
 func (m measure) M(v float64) core.Measurement {
 	return core.Measurement{
 		Measure: m,
@@ -206,7 +210,18 @@ func (m measure) V(v float64) core.KeyValue {
 	return m.rk.Float64(v)
 }
 
-func (m measure) Name() string               { return m.rk.Name() }
-func (m measure) Description() string        { return m.rk.Description() }
-func (m measure) Unit() unit.Unit            { return m.rk.Unit() }
-func (m measure) DefinitionID() core.EventID { return m.rk.DefinitionID() }
+func (m measure) Name() string {
+	return m.rk.Name()
+}
+
+func (m measure) Description() string {
+	return m.rk.Description()
+}
+
+func (m measure) Unit() unit.Unit {
+	return m.rk.Unit()
+}
+
+func (m measure) DefinitionID() core.EventID {
+	return m.rk.DefinitionID()
+}