diff --git a/seskar/seskar-gradle-plugin/src/main/kotlin/seskar/gradle/plugin/IncrementalSyncTask.ext.kt b/seskar/seskar-gradle-plugin/src/main/kotlin/seskar/gradle/plugin/IncrementalSyncTask.ext.kt
index acca4605..e94b6a08 100644
--- a/seskar/seskar-gradle-plugin/src/main/kotlin/seskar/gradle/plugin/IncrementalSyncTask.ext.kt
+++ b/seskar/seskar-gradle-plugin/src/main/kotlin/seskar/gradle/plugin/IncrementalSyncTask.ext.kt
@@ -1,8 +1,11 @@
 package seskar.gradle.plugin
 
 import org.gradle.api.file.Directory
-import org.gradle.api.provider.Provider
+import org.gradle.api.file.DirectoryProperty
+import org.gradle.api.internal.provider.ProviderInternal
 import org.jetbrains.kotlin.gradle.tasks.IncrementalSyncTask
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
 
 private val ORIGINAL_FILE_FILTERS: List<String> =
     GenerationOptions.entries
@@ -15,15 +18,23 @@ internal fun IncrementalSyncTask.excludeOriginalSources() {
 private fun withDirectoryFilter(
     source: Any,
 ): Any {
-    if (source !is Provider<*>)
+    if (!isDirectoryProvider(source))
         return source
 
     return source.map { value ->
-        if (value !is Directory)
-            return@map value
-
         value.asFileTree.matching {
             exclude(ORIGINAL_FILE_FILTERS)
         }
     }
 }
+
+@OptIn(ExperimentalContracts::class)
+private fun isDirectoryProvider(
+    source: Any?,
+): Boolean {
+    contract {
+        returns(true) implies (source is DirectoryProperty)
+    }
+
+    return source is ProviderInternal<*> && source.type == Directory::class.java
+}