diff --git a/user/userns/userns_fuzzer.go b/user/userns/userns_linux_fuzzer.go
similarity index 79%
rename from user/userns/userns_fuzzer.go
rename to user/userns/userns_linux_fuzzer.go
index d90cffc..26ba2e1 100644
--- a/user/userns/userns_fuzzer.go
+++ b/user/userns/userns_linux_fuzzer.go
@@ -1,4 +1,4 @@
-//go:build gofuzz
+//go:build linux && gofuzz
 
 package userns
 
diff --git a/user/userns/userns_unsupported.go b/user/userns/userns_unsupported.go
index 71d4c63..47dd5aa 100644
--- a/user/userns/userns_unsupported.go
+++ b/user/userns/userns_unsupported.go
@@ -7,9 +7,3 @@ package userns
 func runningInUserNS() bool {
 	return false
 }
-
-// uidMapInUserNS is a stub for non-Linux systems
-// Always returns false
-func uidMapInUserNS(uidMap string) bool {
-	return false
-}