diff --git a/project/Build.scala b/project/Build.scala
index 3a614f227e84..119f31775fa4 100644
--- a/project/Build.scala
+++ b/project/Build.scala
@@ -1430,6 +1430,7 @@ object Build {
       Compile / unmanagedSourceDirectories += baseDirectory.value / "src-non-bootstrapped",
       // NOTE: The only difference here is that we drop `-Werror` and semanticDB for now
       Compile / scalacOptions := Seq("-deprecation", "-feature", "-unchecked", "-encoding", "UTF8", "-language:implicitConversions"),
+      Compile / scalacOptions += "-Yexplicit-nulls",
       (Compile / scalacOptions) ++= Seq(
         // Needed so that the library sources are visible when `dotty.tools.dotc.core.Definitions#init` is called
         "-sourcepath", (Compile / sourceDirectories).value.map(_.getCanonicalPath).distinct.mkString(File.pathSeparator),
@@ -1456,6 +1457,7 @@ object Build {
       Compile / unmanagedSourceDirectories += baseDirectory.value / "src-bootstrapped",
       // NOTE: The only difference here is that we drop `-Werror` and semanticDB for now
       Compile / scalacOptions :=  Seq("-deprecation", "-feature", "-unchecked", "-encoding", "UTF8", "-language:implicitConversions"),
+      Compile / scalacOptions += "-Yexplicit-nulls",
       Compile / scalacOptions ++= Seq(
         // Needed so that the library sources are visible when `dotty.tools.dotc.core.Definitions#init` is called
         "-sourcepath", (Compile / sourceDirectories).value.map(_.getCanonicalPath).distinct.mkString(File.pathSeparator),