diff --git a/build.gradle b/build.gradle
index acc8497d..e5abfd76 100644
--- a/build.gradle
+++ b/build.gradle
@@ -199,7 +199,7 @@ tasks.named('test') {
   // To fix this problem, don't use the withPluginClasspath method.
   // Provide a plugin under test with the maven local repository.
   systemProperty("protobufPluginVersion", version)
-  systemProperty("testRepoUrl", testRepoUrl.absolutePath)
+  systemProperty("testRepoUrl", testRepoUrl.toURI().toURL())
   dependsOn(
     "publishProtobufPluginPluginMarkerMavenPublicationToTestRepository",
     "publishPluginMavenPublicationToTestRepository"