diff --git a/pkg/apis/extensions/types.go b/pkg/apis/extensions/types.go
index 8dd49b46654..8ac06701daa 100644
--- a/pkg/apis/extensions/types.go
+++ b/pkg/apis/extensions/types.go
@@ -110,6 +110,8 @@ type DeploymentSpec struct {
 
 	// The number of old ReplicaSets to retain to allow rollback.
 	// This is a pointer to distinguish between explicit zero and not specified.
+	// This is set to the max value of int32 (i.e. 2147483647) by default, which means
+	// "retaining all old ReplicaSets".
 	// +optional
 	RevisionHistoryLimit *int32
 
diff --git a/staging/src/k8s.io/api/extensions/v1beta1/types.go b/staging/src/k8s.io/api/extensions/v1beta1/types.go
index a2b17822c29..b7b9e2a17cd 100644
--- a/staging/src/k8s.io/api/extensions/v1beta1/types.go
+++ b/staging/src/k8s.io/api/extensions/v1beta1/types.go
@@ -151,6 +151,8 @@ type DeploymentSpec struct {
 
 	// The number of old ReplicaSets to retain to allow rollback.
 	// This is a pointer to distinguish between explicit zero and not specified.
+	// This is set to the max value of int32 (i.e. 2147483647) by default, which
+	// means "retaining all old RelicaSets".
 	// +optional
 	RevisionHistoryLimit *int32 `json:"revisionHistoryLimit,omitempty" protobuf:"varint,6,opt,name=revisionHistoryLimit"`