diff --git a/main/src/main/scala/sbt/Defaults.scala b/main/src/main/scala/sbt/Defaults.scala
index 243f10602..186f117b3 100644
--- a/main/src/main/scala/sbt/Defaults.scala
+++ b/main/src/main/scala/sbt/Defaults.scala
@@ -556,7 +556,12 @@ object Defaults extends BuildCommon {
     // Adds subproject build.sbt files to the global list of build files to monitor
     Scope.Global / checkBuildSources / pollInterval :==
       new FiniteDuration(Int.MinValue, TimeUnit.MILLISECONDS),
-    Scope.Global / checkBuildSources / fileInputs += baseDirectory.value.toGlob / "*.sbt",
+    Scope.Global / checkBuildSources / fileInputs ++= {
+      if ((Scope.Global / onChangedBuildSource).value != IgnoreSourceChanges)
+        Seq(baseDirectory.value.toGlob / "*.sbt")
+      else
+        Nil
+    },
   )
 
   lazy val configPaths = sourceConfigPaths ++ resourceConfigPaths ++ outputConfigPaths
diff --git a/main/src/main/scala/sbt/nio/CheckBuildSources.scala b/main/src/main/scala/sbt/nio/CheckBuildSources.scala
index 92930f085..7b3bde263 100644
--- a/main/src/main/scala/sbt/nio/CheckBuildSources.scala
+++ b/main/src/main/scala/sbt/nio/CheckBuildSources.scala
@@ -50,7 +50,7 @@ private[sbt] class CheckBuildSources extends AutoCloseable {
   private val sources = new AtomicReference[Seq[Glob]](Nil)
   private val needUpdate = new AtomicBoolean(true)
   private val lastPolled = new AtomicReference[SDeadline](SDeadline.now)
-  private val previousStamps = new AtomicReference[Seq[(Path, FileStamp)]]
+  private val previousStamps = new AtomicReference[Seq[(Path, FileStamp)]](Nil)
   private[sbt] def fileTreeRepository: Option[FileTreeRepository[FileAttributes]] =
     Option(repository.get)
   private def getStamps(force: Boolean) = {
@@ -66,7 +66,7 @@ private[sbt] class CheckBuildSources extends AutoCloseable {
   private def reset(state: State): Unit = {
     val extracted = Project.extract(state)
     val interval = extracted.get(checkBuildSources / pollInterval)
-    val newSources = extracted.get(Global / checkBuildSources / fileInputs)
+    val newSources = extracted.get(Global / checkBuildSources / fileInputs).distinct
     if (interval >= 0.seconds || "polling" == SysProp.watchMode) {
       Option(repository.getAndSet(null)).foreach(_.close())
       pollingPeriod.set(interval)
@@ -141,26 +141,31 @@ private[sbt] class CheckBuildSources extends AutoCloseable {
                s"modified files: ${modified.mkString("\n  ", "\n  ", "\n")}"
              else "")
           val prefix = rawPrefix.linesIterator.filterNot(_.trim.isEmpty).mkString("\n")
-          if (onChanges == ReloadOnSourceChanges) {
-            val msg = s"$prefix\nReloading sbt..."
-            loggerOrTerminal match {
-              case Right(t) => msg.linesIterator.foreach(l => t.printStream.println(s"[info] $l"))
-              case Left(l)  => l.info(msg)
-            }
-            true
-          } else {
-            val tail = "Apply these changes by running `reload`.\nAutomatically reload the " +
-              "build when source changes are detected by setting " +
-              "`Global / onChangedBuildSource := ReloadOnSourceChanges`.\nDisable this " +
-              "warning by setting `Global / onChangedBuildSource := IgnoreSourceChanges`."
-            val msg = s"$prefix\n$tail"
-            loggerOrTerminal match {
-              case Right(t) =>
-                val prefix = s"[${Def.withColor("warn", Some(AnsiColor.YELLOW), t.isColorEnabled)}]"
-                msg.linesIterator.foreach(l => t.printStream.println(s"$prefix $l"))
-              case Left(l) => l.warn(msg)
-            }
-            false
+
+          onChanges match {
+            case ReloadOnSourceChanges =>
+              val msg = s"$prefix\nReloading sbt..."
+              loggerOrTerminal match {
+                case Right(t) => msg.linesIterator.foreach(l => t.printStream.println(s"[info] $l"))
+                case Left(l)  => l.info(msg)
+              }
+              true
+            case WarnOnSourceChanges =>
+              val tail = "Apply these changes by running `reload`.\nAutomatically reload the " +
+                "build when source changes are detected by setting " +
+                "`Global / onChangedBuildSource := ReloadOnSourceChanges`.\nDisable this " +
+                "warning by setting `Global / onChangedBuildSource := IgnoreSourceChanges`."
+              val msg = s"$prefix\n$tail"
+              loggerOrTerminal match {
+                case Right(t) =>
+                  val prefix =
+                    s"[${Def.withColor("warn", Some(AnsiColor.YELLOW), t.isColorEnabled)}]"
+                  msg.linesIterator.foreach(l => t.printStream.println(s"$prefix $l"))
+                case Left(l) => l.warn(msg)
+              }
+              false
+            case IgnoreSourceChanges =>
+              false
           }
         case _ => false
       }
diff --git a/sbt-app/src/sbt-test/nio/ignore-source-changes/build.sbt b/sbt-app/src/sbt-test/nio/ignore-source-changes/build.sbt
new file mode 100644
index 000000000..c18aacbf4
--- /dev/null
+++ b/sbt-app/src/sbt-test/nio/ignore-source-changes/build.sbt
@@ -0,0 +1,5 @@
+import scala.concurrent.duration.DurationInt
+
+ThisBuild / checkBuildSources / pollInterval := 0.seconds
+
+lazy val sub = project.in(file("sub"))
diff --git a/sbt-app/src/sbt-test/nio/ignore-source-changes/changes/build.1.sbt b/sbt-app/src/sbt-test/nio/ignore-source-changes/changes/build.1.sbt
new file mode 100644
index 000000000..efaf0ec88
--- /dev/null
+++ b/sbt-app/src/sbt-test/nio/ignore-source-changes/changes/build.1.sbt
@@ -0,0 +1,7 @@
+import scala.concurrent.duration.DurationInt
+
+ThisBuild / checkBuildSources / pollInterval := 0.seconds
+
+lazy val sub = project.in(file("sub"))
+
+// change 1
diff --git a/sbt-app/src/sbt-test/nio/ignore-source-changes/changes/build.2.sbt b/sbt-app/src/sbt-test/nio/ignore-source-changes/changes/build.2.sbt
new file mode 100644
index 000000000..f15752646
--- /dev/null
+++ b/sbt-app/src/sbt-test/nio/ignore-source-changes/changes/build.2.sbt
@@ -0,0 +1,7 @@
+import scala.concurrent.duration.DurationInt
+
+ThisBuild / checkBuildSources / pollInterval := 0.seconds
+
+lazy val sub = project.in(file("sub"))
+
+// change 2
diff --git a/sbt-app/src/sbt-test/nio/ignore-source-changes/changes/sub.1.sbt b/sbt-app/src/sbt-test/nio/ignore-source-changes/changes/sub.1.sbt
new file mode 100644
index 000000000..ac0c8f797
--- /dev/null
+++ b/sbt-app/src/sbt-test/nio/ignore-source-changes/changes/sub.1.sbt
@@ -0,0 +1 @@
+// subproject, change 1
diff --git a/sbt-app/src/sbt-test/nio/ignore-source-changes/changes/sub.2.sbt b/sbt-app/src/sbt-test/nio/ignore-source-changes/changes/sub.2.sbt
new file mode 100644
index 000000000..939d56556
--- /dev/null
+++ b/sbt-app/src/sbt-test/nio/ignore-source-changes/changes/sub.2.sbt
@@ -0,0 +1 @@
+// subproject, change 2
diff --git a/sbt-app/src/sbt-test/nio/ignore-source-changes/project/Build.scala b/sbt-app/src/sbt-test/nio/ignore-source-changes/project/Build.scala
new file mode 100644
index 000000000..f9405dd53
--- /dev/null
+++ b/sbt-app/src/sbt-test/nio/ignore-source-changes/project/Build.scala
@@ -0,0 +1,52 @@
+package sbt
+
+import sbt.Keys._
+import sbt.nio.Keys._
+import sbt.internal.util._
+import sbt.util.Level
+
+object Build extends AutoPlugin {
+  val autoImport = Build
+
+  override def trigger = allRequirements
+
+  val awaitsWarn =
+    settingKey[Boolean]("Whether we're checking for warn or not")
+  val checkBuildSourcesWarn =
+    taskKey[Unit]("Checks whether there was a warning or not")
+
+  class CapturingMiniLogger extends MiniLogger {
+    var warnCaptured = false
+    override def log[T](level: Level.Value, message: ObjectEvent[T]): Unit = ()
+    override def log(level: Level.Value, message: => String): Unit =
+      if (level == Level.Warn && message.contains("build source files have changed"))
+        warnCaptured = true
+  }
+
+  override def buildSettings: Seq[Setting[?]] = Seq(
+    awaitsWarn := false,
+    checkBuildSourcesWarn := Def.uncached {
+      val st = state.value
+      val capturing = new CapturingMiniLogger
+      val originalFull = st.globalLogging.full
+      val capturingLogger = new ManagedLogger(
+        originalFull.name,
+        originalFull.channelName,
+        originalFull.execId,
+        capturing
+      )
+      val newLogging = st.globalLogging.copy(full = capturingLogger)
+      val newState = st.copy(globalLogging = newLogging)
+
+      val extractedSt = Project.extract(newState)
+      extractedSt.runTask(checkBuildSources, newState)
+
+      val warnCaptured = capturing.warnCaptured
+      val awaitsWarnValue = extractedSt.get(awaitsWarn)
+      if (warnCaptured != awaitsWarnValue)
+        throw new Exception(
+          s"Warn appeared: ${warnCaptured}; Expected: ${awaitsWarnValue}; See issue #6773"
+        )
+    }
+  )
+}
diff --git a/sbt-app/src/sbt-test/nio/ignore-source-changes/sub/build.sbt b/sbt-app/src/sbt-test/nio/ignore-source-changes/sub/build.sbt
new file mode 100644
index 000000000..b37ae2bff
--- /dev/null
+++ b/sbt-app/src/sbt-test/nio/ignore-source-changes/sub/build.sbt
@@ -0,0 +1 @@
+// subproject
diff --git a/sbt-app/src/sbt-test/nio/ignore-source-changes/test b/sbt-app/src/sbt-test/nio/ignore-source-changes/test
new file mode 100644
index 000000000..c65583311
--- /dev/null
+++ b/sbt-app/src/sbt-test/nio/ignore-source-changes/test
@@ -0,0 +1,24 @@
+> set awaitsWarn := false
+> checkBuildSourcesWarn
+
+> set awaitsWarn := true
+> set Global / onChangedBuildSource := WarnOnSourceChanges
+$ copy-file changes/build.1.sbt build.sbt
+> checkBuildSourcesWarn
+
+> set awaitsWarn := false
+> set Global / onChangedBuildSource := IgnoreSourceChanges
+$ copy-file changes/build.2.sbt build.sbt
+> checkBuildSourcesWarn
+
+# Checking that subproject `.sbt` files are also monitored
+
+> set awaitsWarn := true
+> set Global / onChangedBuildSource := WarnOnSourceChanges
+$ copy-file changes/sub.1.sbt sub/build.sbt
+> checkBuildSourcesWarn
+
+> set awaitsWarn := false
+> set Global / onChangedBuildSource := IgnoreSourceChanges
+$ copy-file changes/sub.2.sbt sub/build.sbt
+> checkBuildSourcesWarn