diff --git a/libcontainer/userns/userns.go b/libcontainer/userns/userns.go
index b225f18f2..069a9bb28 100644
--- a/libcontainer/userns/userns.go
+++ b/libcontainer/userns/userns.go
@@ -1,4 +1,8 @@
 package userns
 
-// RunningInUserNS detects whether we are currently running in a user namespace.
-var RunningInUserNS = runningInUserNS
+// RunningInUserNS detects whether we are currently running in a Linux
+// user namespace and memoizes the result. It returns false on non-Linux
+// platforms.
+func RunningInUserNS() bool {
+	return runningInUserNS()
+}