diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 03de17c..47905d2 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -12,7 +12,7 @@ jobs:
         run: sbt scalafmtCheckAll "rules/scalafix --check"
 
       - name: Test
-        run: sbt coverage tests/test rules/coverageReport
+        run: sbt coverage +tests/test +rules/coverageReport
 
       - uses: codecov/codecov-action@v1
         with:
diff --git a/.github/workflows/release.yaml b/.github/workflows/release.yaml
index fcd50c1..60d45d1 100644
--- a/.github/workflows/release.yaml
+++ b/.github/workflows/release.yaml
@@ -11,7 +11,7 @@ jobs:
       - uses: olafurpg/setup-scala@v2
       - uses: olafurpg/setup-gpg@v2
       - name: Publish ${{ github.ref }}
-        run: sbt scalafmtCheck "rules/scalafix --check" test ci-release
+        run: sbt scalafmtCheck "rules/scalafix --check" +test ci-release
         env:
           PGP_PASSPHRASE: ${{ secrets.PGP_PASSPHRASE }}
           PGP_SECRET: ${{ secrets.PGP_SECRET }}
diff --git a/build.sbt b/build.sbt
index 682e7be..939d218 100644
--- a/build.sbt
+++ b/build.sbt
@@ -14,7 +14,9 @@ inThisBuild(
       )
     ),
     scalaVersion := v.scala212,
+    crossScalaVersions := List(v.scala212, v.scala213),
     scalacOptions ++= List(
+      "-deprecation",
       "-Yrangepos",
       "-P:semanticdb:synthetics:on"
     ),
@@ -22,7 +24,8 @@ inThisBuild(
     dependencyOverrides ++= List(
       "org.scala-lang.modules" %% "scala-xml" % "1.2.0",
       "org.slf4j" % "slf4j-api" % "1.7.25",
-      "com.lihaoyi" %% "sourcecode" % "0.2.1"
+      "com.lihaoyi" %% "sourcecode" % "0.2.1",
+      "org.scala-lang.modules" %% "scala-collection-compat" % "2.1.6"
     ),
     addCompilerPlugin(scalafixSemanticdb),
     scalafixDependencies += "com.github.liancheng" %% "organize-imports" % "0.3.1-RC2",
diff --git a/rules/src/main/scala/fix/OrganizeImports.scala b/rules/src/main/scala/fix/OrganizeImports.scala
index 3fc0e00..16c44aa 100644
--- a/rules/src/main/scala/fix/OrganizeImports.scala
+++ b/rules/src/main/scala/fix/OrganizeImports.scala
@@ -228,16 +228,15 @@ class OrganizeImports(config: OrganizeImportsConfig) extends SemanticRule("Organ
     else importer.copy(ref = toRef(importer.ref.symbol))
   }
 
-  private def groupImporters(importers: Seq[Importer]): Seq[Seq[Importer]] = {
-    val (_, importerGroups) = importers
+  private def groupImporters(importers: Seq[Importer]): Seq[Seq[Importer]] =
+    importers
       .groupBy(matchImportGroup) // Groups imports by importer prefix.
-      .mapValues(organizeImportGroup) // Organize imports within the same group.
       .toSeq
       .sortBy { case (index, _) => index } // Sorts import groups by group index
-      .unzip
-
-    importerGroups
-  }
+      .map {
+        // Organize imports within the same group.
+        case (_, importers) => organizeImportGroup(importers)
+      }
 
   private def organizeImportGroup(importers: Seq[Importer]): Seq[Importer] = {
     val importeesSorted = {
@@ -261,12 +260,12 @@ class OrganizeImports(config: OrganizeImportsConfig) extends SemanticRule("Organ
 
       importer match {
         case Importer(_, Importee.Wildcard() :: Nil) =>
-          syntax.patch(syntax.lastIndexOfSlice("._"), ".\0", 2)
+          syntax.patch(syntax.lastIndexOfSlice("._"), ".\u0000", 2)
 
         case _ if isCurlyBraced(importer) =>
           syntax
-            .replaceFirst("[{]", "\2")
-            .patch(syntax.lastIndexOf("}"), "\2", 1)
+            .replaceFirst("[{]", "\u0002")
+            .patch(syntax.lastIndexOf("}"), "\u0002", 1)
 
         case _ => syntax
       }
@@ -442,8 +441,7 @@ object OrganizeImports {
         val allRenames = allImportees
           .filter(_.is[Importee.Rename])
           .groupBy { case Importee.Rename(Name(name), _) => name }
-          .mapValues(_.head)
-          .values
+          .map { case (_, importees) => importees.head }
           .toList
 
         // Collects distinct explicitly imported names, and filters out those that are also renamed.
@@ -464,8 +462,7 @@ object OrganizeImports {
         val (renamedNames, importedNames) = allImportees
           .filter(_.is[Importee.Name])
           .groupBy { case Importee.Name(Name(name)) => name }
-          .mapValues(_.head)
-          .values
+          .map { case (_, importees) => importees.head }
           .toList
           .partition {
             case Importee.Name(Name(name)) =>
@@ -598,7 +595,7 @@ object OrganizeImports {
       importGroups
         .map(prettyPrintImportGroup)
         .mkString("\n\n")
-        .lines
+        .linesIterator
         .zipWithIndex
         .map {
           // The first line will be inserted at an already indented position.
diff --git a/rules/src/main/scala/fix/OrganizeImportsConfig.scala b/rules/src/main/scala/fix/OrganizeImportsConfig.scala
index b8e0fd7..88c55f5 100644
--- a/rules/src/main/scala/fix/OrganizeImportsConfig.scala
+++ b/rules/src/main/scala/fix/OrganizeImportsConfig.scala
@@ -14,9 +14,9 @@ object ImportsOrder {
   case object Keep extends ImportsOrder
 
   implicit def reader: ConfDecoder[ImportsOrder] =
-    ReaderUtil.fromMap {
-      List(Ascii, SymbolsFirst, Keep) groupBy (_.toString) mapValues (_.head)
-    }
+    ReaderUtil.fromMap(
+      (List(Ascii, SymbolsFirst, Keep) map (v => v.toString -> v)).toMap
+    )
 }
 
 sealed trait ImportSelectorsOrder
@@ -28,7 +28,7 @@ object ImportSelectorsOrder {
 
   implicit def reader: ConfDecoder[ImportSelectorsOrder] =
     ReaderUtil.fromMap {
-      List(Ascii, SymbolsFirst, Keep) groupBy (_.toString) mapValues (_.head)
+      (List(Ascii, SymbolsFirst, Keep) map (v => v.toString -> v)).toMap
     }
 }
 
@@ -41,7 +41,7 @@ object GroupedImports {
 
   implicit def reader: ConfDecoder[GroupedImports] =
     ReaderUtil.fromMap {
-      List(Merge, Explode, Keep) groupBy (_.toString) mapValues (_.head)
+      (List(Merge, Explode, Keep) map (v => v.toString -> v)).toMap
     }
 }