diff --git a/.circleci/config.yml b/.circleci/config.yml
index 639118c93..715992acd 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -85,7 +85,7 @@ workflows:
       - scala_job:
           name: dotty
           java_version: jdk8
-          scala_version: 0.17.0-RC1
+          scala_version: 0.18.1-RC1
       - scala_job:
           name: jdk11_2.12.9
           java_version: jdk11
@@ -97,7 +97,7 @@ workflows:
       - scala_job:
           name: jdk11_dotty
           java_version: jdk11
-          scala_version: 0.17.0-RC1
+          scala_version: 0.18.1-RC1
       - scalajs_job:
           name: sjs0.6_2.12
           scala_version: 2.12.9
diff --git a/.travis.yml b/.travis.yml
index 7a6500752..bfb72d9e6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,7 +3,7 @@ language: scala
 scala:
   - 2.12.9
   - 2.13.0
-  - 0.17.0-RC1
+  - 0.18.1-RC1
 
 env:
   global:
@@ -22,9 +22,9 @@ env:
 
 matrix:
   exclude:
-    - scala: 0.17.0-RC1
+    - scala: 0.18.1-RC1
       env: SCALAJS_VERSION=0.6.28   ADOPTOPENJDK=8
-    - scala: 0.17.0-RC1
+    - scala: 0.18.1-RC1
       env: SCALAJS_VERSION=1.0.0-M8 ADOPTOPENJDK=8
 
 before_install:
diff --git a/build.sbt b/build.sbt
index a9d546eb0..bf2eb7c83 100644
--- a/build.sbt
+++ b/build.sbt
@@ -11,6 +11,7 @@ lazy val configSettings: Seq[Setting[_]] = Seq(
       Seq(
         CrossVersion.partialVersion(sv) match {
           case Some((2, 13)) => file(dir.getPath ++ "-2.13+")
+          case Some((0, _))  => file(dir.getPath ++ "-2.13+")
           case _             => file(dir.getPath ++ "-2.13-")
         },
         CrossVersion.partialVersion(sv) match {
@@ -30,7 +31,7 @@ lazy val xml = crossProject(JSPlatform, JVMPlatform)
   .settings(scalaModuleSettings)
   .jvmSettings(scalaModuleSettingsJVM)
   .jvmSettings(
-    crossScalaVersions += "0.17.0-RC1"
+    crossScalaVersions += "0.18.1-RC1"
   )
   .settings(
     name    := "scala-xml",
diff --git a/shared/src/main/scala/scala/xml/dtd/impl/Base.scala b/shared/src/main/scala/scala/xml/dtd/impl/Base.scala
index 3283e2ba0..7bfb995d6 100644
--- a/shared/src/main/scala/scala/xml/dtd/impl/Base.scala
+++ b/shared/src/main/scala/scala/xml/dtd/impl/Base.scala
@@ -20,7 +20,7 @@ private[dtd] abstract class Base {
   type _regexpT <: RegExp
 
   abstract class RegExp {
-    val isNullable: Boolean
+    def isNullable: Boolean
   }
 
   object Alt {