diff --git a/compiler/src/dotty/tools/dotc/reporting/Diagnostic.scala b/compiler/src/dotty/tools/dotc/reporting/Diagnostic.scala
index 6f84965ba092..b22937302b2c 100644
--- a/compiler/src/dotty/tools/dotc/reporting/Diagnostic.scala
+++ b/compiler/src/dotty/tools/dotc/reporting/Diagnostic.scala
@@ -112,5 +112,5 @@ class Diagnostic(
   override def diagnosticRelatedInformation: JList[interfaces.DiagnosticRelatedInformation] =
     Collections.emptyList()
 
-  override def toString: String = s"$getClass at $pos: $message"
+  override def toString: String = s"$getClass at $pos L${pos.line}: $message"
 end Diagnostic
diff --git a/project/Build.scala b/project/Build.scala
index a7be508ce11a..fbf3dc843d82 100644
--- a/project/Build.scala
+++ b/project/Build.scala
@@ -292,7 +292,9 @@ object Build {
       "-deprecation",
       "-unchecked",
       //"-Wconf:cat=deprecation&msg=Unsafe:s",    // example usage
-      "-Xfatal-warnings",                         // -Werror in modern usage
+      "-Werror",
+      //"-Wunused:all",
+      //"-rewrite", // requires -Werror:false since no rewrites are applied with errors
       "-encoding", "UTF8",
       "-language:implicitConversions",
     ),
@@ -1224,8 +1226,8 @@ object Build {
       },
       Compile / doc / scalacOptions += "-Ydocument-synthetic-types",
       scalacOptions += "-Ycompile-scala2-library",
-      scalacOptions += "-Yscala2Unpickler:never",
-      scalacOptions -= "-Xfatal-warnings",
+      scalacOptions += "-Yscala2-unpickler:never",
+      scalacOptions -= "-Werror",
       Compile / compile / logLevel.withRank(KeyRanks.Invisible) := Level.Error,
       ivyConfigurations += SourceDeps.hide,
       transitiveClassifiers := Seq("sources"),
@@ -1596,7 +1598,7 @@ object Build {
     dependsOn(`scala3-library-bootstrappedJS`).
     settings(
       bspEnabled := false,
-      scalacOptions --= Seq("-Xfatal-warnings", "-deprecation"),
+      scalacOptions --= Seq("-Werror", "-deprecation"),
 
       // Required to run Scala.js tests.
       Test / fork := false,