diff --git a/compiler/src/dotty/tools/dotc/cc/ccConfig.scala b/compiler/src/dotty/tools/dotc/cc/ccConfig.scala
index 27ddd0c923be..81e4b6b46bbf 100644
--- a/compiler/src/dotty/tools/dotc/cc/ccConfig.scala
+++ b/compiler/src/dotty/tools/dotc/cc/ccConfig.scala
@@ -48,7 +48,7 @@ object ccConfig:
 
   /** If true, turn on separation checking */
   def useSepChecks(using Context): Boolean =
-    Feature.sourceVersion.stable.isAtLeast(SourceVersion.`3.7`)
+    Feature.sourceVersion.stable.isAtLeast(SourceVersion.`3.8`)
 
   /** If true, do level checking for FreshCap instances */
   def useFreshLevels(using Context): Boolean =
@@ -58,4 +58,4 @@ object ccConfig:
   def newScheme(using Context): Boolean =
     Feature.sourceVersion.stable.isAtLeast(SourceVersion.`3.7`)
 
-end ccConfig
\ No newline at end of file
+end ccConfig
diff --git a/compiler/test/dotty/tools/dotc/CompilationTests.scala b/compiler/test/dotty/tools/dotc/CompilationTests.scala
index 93238647d1a3..2d2f01388374 100644
--- a/compiler/test/dotty/tools/dotc/CompilationTests.scala
+++ b/compiler/test/dotty/tools/dotc/CompilationTests.scala
@@ -37,7 +37,7 @@ class CompilationTests {
       compileFilesInDir("tests/pos-special/sourcepath/outer", defaultOptions.and("-sourcepath", "tests/pos-special/sourcepath")),
       compileFile("tests/pos-special/sourcepath/outer/nested/Test4.scala", defaultOptions.and("-sourcepath", "tests/pos-special/sourcepath")),
       compileFilesInDir("tests/pos-scala2", defaultOptions.and("-source", "3.0-migration")),
-      compileFilesInDir("tests/pos-custom-args/captures", defaultOptions.and("-language:experimental.captureChecking")),
+      compileFilesInDir("tests/pos-custom-args/captures", defaultOptions.and("-language:experimental.captureChecking", "-source", "3.8")),
       compileFile("tests/pos-special/utf8encoded.scala", defaultOptions.and("-encoding", "UTF8")),
       compileFile("tests/pos-special/utf16encoded.scala", defaultOptions.and("-encoding", "UTF16")),
       compileDir("tests/pos-special/i18589", defaultOptions.and("-Wsafe-init").without("-Ycheck:all")),
@@ -146,7 +146,7 @@ class CompilationTests {
     aggregateTests(
       compileFilesInDir("tests/neg", defaultOptions, FileFilter.exclude(TestSources.negScala2LibraryTastyExcludelisted)),
       compileFilesInDir("tests/neg-deep-subtype", allowDeepSubtypes),
-      compileFilesInDir("tests/neg-custom-args/captures", defaultOptions.and("-language:experimental.captureChecking")),
+      compileFilesInDir("tests/neg-custom-args/captures", defaultOptions.and("-language:experimental.captureChecking", "-source", "3.8")),
       compileFile("tests/neg-custom-args/sourcepath/outer/nested/Test1.scala", defaultOptions.and("-sourcepath", "tests/neg-custom-args/sourcepath")),
       compileDir("tests/neg-custom-args/sourcepath2/hi", defaultOptions.and("-sourcepath", "tests/neg-custom-args/sourcepath2", "-Xfatal-warnings")),
       compileList("duplicate source", List(
@@ -169,7 +169,7 @@ class CompilationTests {
     aggregateTests(
       compileFilesInDir("tests/run", defaultOptions.and("-Wsafe-init")),
       compileFilesInDir("tests/run-deep-subtype", allowDeepSubtypes),
-      compileFilesInDir("tests/run-custom-args/captures", allowDeepSubtypes.and("-language:experimental.captureChecking")),
+      compileFilesInDir("tests/run-custom-args/captures", allowDeepSubtypes.and("-language:experimental.captureChecking", "-source", "3.8")),
       // Run tests for legacy lazy vals.
       compileFilesInDir("tests/run", defaultOptions.and("-Wsafe-init", "-Ylegacy-lazy-vals", "-Ycheck-constraint-deps"), FileFilter.include(TestSources.runLazyValsAllowlist)),
     ).checkRuns()
diff --git a/project/Build.scala b/project/Build.scala
index 0c057b6a7884..5cb1785b6938 100644
--- a/project/Build.scala
+++ b/project/Build.scala
@@ -1236,7 +1236,10 @@ object Build {
     withCommonSettings(Bootstrapped).
     dependsOn(dottyCompiler(Bootstrapped) % "provided; compile->runtime; test->test").
     settings(scala2LibraryBootstrappedSettings).
-    settings(moduleName := "scala2-library-cc")
+    settings(
+      moduleName := "scala2-library-cc",
+      scalacOptions ++= Seq("-source", "3.8"), // for separation checking
+    )
 
   lazy val scala2LibraryBootstrappedSettings = Seq(
       javaOptions := (`scala3-compiler-bootstrapped` / javaOptions).value,