diff --git a/src/partest/scala/tools/partest/nest/Runner.scala b/src/partest/scala/tools/partest/nest/Runner.scala
index 990ed6be347a..d5c63ed442ea 100644
--- a/src/partest/scala/tools/partest/nest/Runner.scala
+++ b/src/partest/scala/tools/partest/nest/Runner.scala
@@ -453,10 +453,12 @@ class Runner(val testInfo: TestInfo, val suiteRunner: AbstractRunner) {
   }
 
   // all sources in a round may contribute flags via // scalac: -flags
+  // if a javaVersion isn't specified, require the minimum viable using -release 8 to avoid gotcha in CI.
   def flagsForCompilation(sources: List[File]): List[String] = {
-    val perFile = toolArgsFor(sources)("scalac")
-    if (parentFile.getParentFile.getName == "macro-annot") "-Ymacro-annotations" :: perFile
-    else perFile
+    var perFile = toolArgsFor(sources)("scalac")
+    if (parentFile.getParentFile.getName == "macro-annot") perFile ::= "-Ymacro-annotations"
+    if (toolArgsFor(sources)("javaVersion", split = false).isEmpty) perFile :::= List("-release", "8")
+    perFile
   }
 
   // inspect sources for tool args