diff --git a/src/main/scala/sbtghactions/GenerativePlugin.scala b/src/main/scala/sbtghactions/GenerativePlugin.scala
index 6ccc50c..2ea4be9 100644
--- a/src/main/scala/sbtghactions/GenerativePlugin.scala
+++ b/src/main/scala/sbtghactions/GenerativePlugin.scala
@@ -282,12 +282,16 @@ ${indent(rendered.mkString("\n"), 1)}"""
       case sbtStep: Sbt =>
         import sbtStep.commands
 
-        val multi = (sbtStepPreamble ::: commands) match {
+        // Arguments starting with '-' (-D..., -J..., -v) are options for the sbt launcher, not
+        // commands; inside the command string sbt would try to run them, so they stay separate.
+        val (launcherOptions, sbtCommands) = (sbtStepPreamble ::: commands).partition(_.startsWith("-"))
+        val renderedOptions = launcherOptions.map(o => if (o.indexOf(' ') >= 0) s"'$o'" else o)
+        val multi = sbtCommands match {
           case x :: Nil => x
           case xs       => s"'${xs.mkString("; ")}'"
         }
         renderRunBody(
-          commands = List(s"$sbt $multi"),
+          commands = List((sbt :: renderedOptions ::: List(multi)).mkString(" ")),
           params = sbtStep.params,
           renderedShell = renderedShell
         )
diff --git a/src/test/scala/sbtghactions/GenerativePluginSpec.scala b/src/test/scala/sbtghactions/GenerativePluginSpec.scala
index 0bd4dcc..ee232be 100644
--- a/src/test/scala/sbtghactions/GenerativePluginSpec.scala
+++ b/src/test/scala/sbtghactions/GenerativePluginSpec.scala
@@ -442,6 +442,18 @@ class GenerativePluginSpec extends Specification {
         sbtStepPreamble = Nil) mustEqual s"- run: $$SBT ci-release"
     }
 
+    "keep sbt launcher options out of the command string" in {
+      compileStep(
+        Sbt(List("-Dslick.testkit-config=test-dbs/testkit-github.conf", "test")),
+        "$SBT") mustEqual s"- run: $$SBT -Dslick.testkit-config=test-dbs/testkit-github.conf '++ $${{ matrix.scala }}; test'"
+    }
+
+    "quote sbt launcher options containing spaces" in {
+      compileStep(
+        Sbt(List("-Dgreeting=hello world", "test")),
+        "$SBT") mustEqual s"- run: $$SBT '-Dgreeting=hello world' '++ $${{ matrix.scala }}; test'"
+    }
+
     "compile sbt with parameters" in {
       compileStep(
         Sbt(List("compile", "test"), params = Map("abc" -> "def", "cafe" -> "@42")),