diff --git a/README.md b/README.md
index 5936399..cccd306 100644
--- a/README.md
+++ b/README.md
@@ -29,7 +29,7 @@ collections (`List`, `Vector`, `Seq`, `Set`, `Map`).
 ### scala-cli
 
 ```scala
-//> using scala 3.9.0-RC4
+//> using scala 3.9.0
 //> using dep com.halotukozak::mcodec::<version>
 ```
 
@@ -43,7 +43,7 @@ libraryDependencies += "com.halotukozak" %% "mcodec" % "<version>"
 ### mill
 
 ```scala
-def scalaVersion = "3.9.0-RC4"
+def scalaVersion = "3.9.0"
 def mvDeps = Seq(mvn"com.halotukozak::mcodec::<version>")
 ```
 
diff --git a/project.scala b/project.scala
index 3ff90c6..e56059e 100644
--- a/project.scala
+++ b/project.scala
@@ -1,6 +1,6 @@
-//> using scala 3.9.0-RC6
+//> using scala 3.9.0
 
-//> using dep com.halotukozak::made::0.4.0
+//> using dep com.halotukozak::made::0.4.1
 
 //> using test.dep org.scalameta::munit::1.3.5
 //> using test.dep org.scalameta::munit-scalacheck::1.3.0
diff --git a/test/mcodec/BsonRoundTripTest.scala b/test/mcodec/BsonRoundTripTest.scala
index eb7ee2a..4eda3f3 100644
--- a/test/mcodec/BsonRoundTripTest.scala
+++ b/test/mcodec/BsonRoundTripTest.scala
@@ -13,6 +13,14 @@ class BsonRoundTripTest extends RoundTrip(BsonBackend):
 
   given Arbitrary[Double] = Arbitrary(Arbitrary.arbitrary[Double].suchThat(java.lang.Double.isFinite))
 
+  // BSON field names are cstrings and cannot contain a NUL byte (see BsonOutput.writeCString).
+  given Arbitrary[Map[String, Int]] = Arbitrary(
+    Gen.mapOf(for
+      k <- Arbitrary.arbitrary[String].map(_.filterNot(_ == '\u0000'))
+      v <- Arbitrary.arbitrary[Int]
+    yield k -> v),
+  )
+
   // FlatShape Arbitrary — copy from FlatDiscriminatorTest (that given is scoped to its own suite).
   given Arbitrary[FlatShape] = Arbitrary(
     Gen.oneOf(