diff --git a/internal/zinc-apiinfo/src/main/scala/sbt/internal/inc/ClassToAPI.scala b/internal/zinc-apiinfo/src/main/scala/sbt/internal/inc/ClassToAPI.scala
index 2a91f0cf8..693a0523f 100644
--- a/internal/zinc-apiinfo/src/main/scala/sbt/internal/inc/ClassToAPI.scala
+++ b/internal/zinc-apiinfo/src/main/scala/sbt/internal/inc/ClassToAPI.scala
@@ -507,11 +507,11 @@ object ClassToAPI {
    * We need this logic to trigger recompilation due to changes to pattern exhaustivity checking results.
    */
   private def childrenOfSealedClass(c: Class[?]): Seq[api.Type] =
-    if (!c.isEnum) emptyTypeArray
+    if (!c.isEnum) emptyTypeArray.toIndexedSeq
     else {
       // Calling getCanonicalName() on classes from enum constants yields same string as enumClazz.getCanonicalName
       // Moreover old behaviour create new instance of enum - what may fail (e.g. in static block )
-      Array(reference(c))
+      Seq(reference(c))
     }
 
   // full information not available from reflection
@@ -556,7 +556,7 @@ object ClassToAPI {
     }
 
   def pathFromString(s: String): api.Path =
-    pathFromStrings(s.split("\\."))
+    pathFromStrings(s.split("\\.").toIndexedSeq)
   def pathFromStrings(ss: Seq[String]): api.Path =
     api.Path.of((ss.map(api.Id.of(_)) :+ ThisRef).toArray)
   def packageName(c: Class[?]) = packageAndName(c)._1
diff --git a/internal/zinc-apiinfo/src/main/scala/xsbt/api/Discovery.scala b/internal/zinc-apiinfo/src/main/scala/xsbt/api/Discovery.scala
index 608a1c8da..9801e89e3 100644
--- a/internal/zinc-apiinfo/src/main/scala/xsbt/api/Discovery.scala
+++ b/internal/zinc-apiinfo/src/main/scala/xsbt/api/Discovery.scala
@@ -34,13 +34,13 @@ class Discovery(baseClasses: Set[String], annotations: Set[String]) {
       case _ => Discovered.empty
     }
   def discover(c: ClassLike): Discovered = {
-    val onClass = Discovery.findAnnotations(c.annotations, annotations)
+    val onClass = Discovery.findAnnotations(c.annotations.toIndexedSeq, annotations)
     val onDefs = Discovery.defAnnotations(c.structure, annotations) ++ c.savedAnnotations.filter(
       annotations
     )
     val module = isModule(c)
     new Discovered(
-      bases(c.name, c.structure.parents),
+      bases(c.name, c.structure.parents.toIndexedSeq),
       onClass ++ onDefs,
       module && hasMainMethod(c),
       module
@@ -66,7 +66,7 @@ object Discovery {
       simpleName(a.base).filter(pred)
     }.toSet
   def defAnnotations(s: Structure, pred: String => Boolean): Set[String] =
-    defAnnotations(s.declared, pred) ++ defAnnotations(s.inherited, pred)
+    defAnnotations(s.declared.toIndexedSeq, pred) ++ defAnnotations(s.inherited, pred)
   def defAnnotations(defs: Seq[Definition], pred: String => Boolean): Set[String] =
     findAnnotations(
       defs.flatMap {
@@ -82,19 +82,21 @@ object Discovery {
   def isModule(c: ClassLike) = c.definitionType == DefinitionType.Module
 
   def hasMainMethod(c: ClassLike): Boolean =
-    hasMainMethod(c.structure.declared) || hasMainMethod(c.structure.inherited)
+    hasMainMethod(c.structure.declared.toIndexedSeq) || hasMainMethod(
+      c.structure.inherited.toIndexedSeq
+    )
   def hasMainMethod(defs: Seq[Definition]): Boolean =
     defs.exists(isMainMethod)
   def isMainMethod(d: Definition): Boolean =
     d match {
       case d: Def =>
         d.name == "main" && isPublic(d) && isConcrete(d) && isUnit(d.returnType) && isStringArray(
-          d.valueParameters
+          d.valueParameters.toIndexedSeq
         )
       case _ => false
     }
   def isStringArray(vp: IndexedSeq[ParameterList]): Boolean =
-    vp.length == 1 && isStringArray(vp(0).parameters)
+    vp.length == 1 && isStringArray(vp(0).parameters.toIndexedSeq)
   def isStringArray(params: Seq[MethodParameter]): Boolean =
     params.length == 1 && isStringArray(params(0))
   def isStringArray(p: MethodParameter): Boolean =
diff --git a/internal/zinc-apiinfo/src/main/scala/xsbt/api/ShowAPI.scala b/internal/zinc-apiinfo/src/main/scala/xsbt/api/ShowAPI.scala
index 3c706b8b6..14ae4f456 100644
--- a/internal/zinc-apiinfo/src/main/scala/xsbt/api/ShowAPI.scala
+++ b/internal/zinc-apiinfo/src/main/scala/xsbt/api/ShowAPI.scala
@@ -41,12 +41,14 @@ object ShowAPI {
     case v: Val => showMonoDef(v, "val") + ": " + showType(v.tpe)
     case v: Var => showMonoDef(v, "var") + ": " + showType(v.tpe)
     case d: Def =>
-      showPolyDef(d, "def") + showValueParams(d.valueParameters) + ": " + showType(d.returnType)
+      showPolyDef(d, "def") + showValueParams(d.valueParameters.toIndexedSeq) + ": " + showType(
+        d.returnType
+      )
     case ta: TypeAlias       => showPolyDef(ta, "type") + " = " + showType(ta.tpe)
     case td: TypeDeclaration => showPolyDef(td, "type") + showBounds(td.lowerBound, td.upperBound)
     case cl: ClassLike =>
       showMonoDef(d, showDefinitionType(cl.definitionType)) +
-        showTypeParameters(cl.typeParameters) + " extends " + showTemplate(cl)
+        showTypeParameters(cl.typeParameters.toIndexedSeq) + " extends " + showTemplate(cl)
     case cl: ClassLikeDef => showPolyDef(cl, showDefinitionType(cl.definitionType))
   }
 
@@ -59,9 +61,11 @@ object ShowAPI {
 
       cl.structure.parents.map(showNestedType).mkString("", " with ", " {") + showSelf +
         lines(
-          truncateDecls(cl.structure.inherited).map(d => "^inherited^ " + showNestedDefinition(d))
+          truncateDecls(cl.structure.inherited).toIndexedSeq.map(d =>
+            "^inherited^ " + showNestedDefinition(d)
+          )
         ) +
-        lines(truncateDecls(cl.structure.declared).map(showNestedDefinition)) +
+        lines(truncateDecls(cl.structure.declared).toIndexedSeq.map(showNestedDefinition)) +
         "}"
     }
 
@@ -73,7 +77,7 @@ object ShowAPI {
     case p: Parameterized =>
       showType(p.baseType) + p.typeArguments.map(showType).mkString("[", ", ", "]")
     case c: Constant  => showType(c.baseType) + "(" + c.value + ")"
-    case a: Annotated => showAnnotations(a.annotations) + " " + showType(a.baseType)
+    case a: Annotated => showAnnotations(a.annotations.toIndexedSeq) + " " + showType(a.baseType)
     case s: Structure =>
       s.parents.map(showType).mkString(" with ") + (
         if (nesting <= 0) "{ <nesting level reached> }"
@@ -90,7 +94,7 @@ object ShowAPI {
     case p: Polymorphic =>
       showType(p.baseType) + (
         if (nesting <= 0) " [ <nesting level reached> ]"
-        else showNestedTypeParameters(p.parameters)
+        else showNestedTypeParameters(p.parameters.toIndexedSeq)
       )
   }
 
@@ -103,22 +107,22 @@ object ShowAPI {
 
   private def space(s: String) = if (s.isEmpty) s else s + " "
   private def showMonoDef(d: Definition, label: String)(implicit nesting: Int): String =
-    space(showAnnotations(d.annotations)) + space(showAccess(d.access)) + space(
+    space(showAnnotations(d.annotations.toIndexedSeq)) + space(showAccess(d.access)) + space(
       showModifiers(d.modifiers)
     ) + space(label) + d.name
 
   private def showPolyDef(d: ParameterizedDefinition, label: String)(
       implicit nesting: Int
   ): String =
-    showMonoDef(d, label) + showTypeParameters(d.typeParameters)
+    showMonoDef(d, label) + showTypeParameters(d.typeParameters.toIndexedSeq)
 
   private def showTypeParameters(tps: Seq[TypeParameter])(implicit nesting: Int): String =
     if (tps.isEmpty) ""
     else tps.map(showTypeParameter).mkString("[", ", ", "]")
 
   private def showTypeParameter(tp: TypeParameter)(implicit nesting: Int): String =
-    showAnnotations(tp.annotations) + " " + showVariance(tp.variance) + tp.id + showTypeParameters(
-      tp.typeParameters
+    showAnnotations(tp.annotations.toIndexedSeq) + " " + showVariance(tp.variance) + tp.id + showTypeParameters(
+      tp.typeParameters.toIndexedSeq
     ) + " " + showBounds(tp.lowerBound, tp.upperBound)
 
   private def showAnnotations(as: Seq[Annotation])(implicit nesting: Int) =
diff --git a/internal/zinc-compile-core/src/main/scala/sbt/internal/inc/CompilerArguments.scala b/internal/zinc-compile-core/src/main/scala/sbt/internal/inc/CompilerArguments.scala
index f490e9150..c6834ada4 100644
--- a/internal/zinc-compile-core/src/main/scala/sbt/internal/inc/CompilerArguments.scala
+++ b/internal/zinc-compile-core/src/main/scala/sbt/internal/inc/CompilerArguments.scala
@@ -88,7 +88,8 @@ final class CompilerArguments(
    */
   def finishClasspath(classpath: Seq[Path]): Seq[Path] = {
     val filteredClasspath = filterLibrary(classpath)
-    val extraCompiler = include(cpOptions.compiler, scalaInstance.compilerJars.map(_.toPath): _*)
+    val extraCompiler =
+      include(cpOptions.compiler, scalaInstance.compilerJars.toIndexedSeq.map(_.toPath): _*)
     val otherJars = scalaInstance.otherJars.toList.map(_.toPath)
     val extraClasspath = include(cpOptions.extra, otherJars: _*)
     filteredClasspath ++ extraCompiler ++ extraClasspath