diff --git a/backend/build.gradle b/backend/build.gradle
index 8690982d8..47dab440a 100644
--- a/backend/build.gradle
+++ b/backend/build.gradle
@@ -114,7 +114,7 @@ def generatedSrcDir = new File(buildDir, 'generated/src/main/java')
 sourceSets {
     main {
         groovy {
-            srcDirs += ['src/main/groovy', 'src/main/java', generatedSrcDir]
+            srcDirs = ['src/main/groovy', 'src/main/java', generatedSrcDir]
         }
         java {
             srcDirs = []