diff --git a/runners/gradle-plugin/src/main/kotlin/org/jetbrains/dokka/gradle/kotlin/isMainSourceSet.kt b/runners/gradle-plugin/src/main/kotlin/org/jetbrains/dokka/gradle/kotlin/isMainSourceSet.kt
index 15989217b32..e21e22bbd9c 100644
--- a/runners/gradle-plugin/src/main/kotlin/org/jetbrains/dokka/gradle/kotlin/isMainSourceSet.kt
+++ b/runners/gradle-plugin/src/main/kotlin/org/jetbrains/dokka/gradle/kotlin/isMainSourceSet.kt
@@ -5,6 +5,7 @@ import com.android.build.gradle.api.LibraryVariant
 import org.gradle.api.Project
 import org.jetbrains.kotlin.gradle.plugin.KotlinSourceSet
 import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinJvmAndroidCompilation
+import java.util.Locale
 
 internal fun Project.isMainSourceSet(sourceSet: KotlinSourceSet): Boolean {
     return isMainSourceSet(allCompilationsOf(sourceSet))
@@ -22,8 +23,7 @@ private fun isMainCompilation(compilation: KotlinCompilation): Boolean {
             return androidVariant is LibraryVariant || androidVariant is ApplicationVariant
         }
     } catch (e: NoSuchMethodError) {
-        // Kotlin Plugin version below 1.4
-        return !compilation.name.toLowerCase().endsWith("test")
+        return !compilation.name.lowercase(Locale.getDefault()).endsWith("test")
     }
     return compilation.name == "main"
 }