diff --git a/dataforge-workspace/src/jvmMain/kotlin/space/kscience/dataforge/workspace/FileWorkspaceCache.kt b/dataforge-workspace/src/jvmMain/kotlin/space/kscience/dataforge/workspace/FileWorkspaceCache.kt
index 5d17baf3..fdcb49a6 100644
--- a/dataforge-workspace/src/jvmMain/kotlin/space/kscience/dataforge/workspace/FileWorkspaceCache.kt
+++ b/dataforge-workspace/src/jvmMain/kotlin/space/kscience/dataforge/workspace/FileWorkspaceCache.kt
@@ -4,6 +4,7 @@ import io.ktor.utils.io.core.Input
 import io.ktor.utils.io.core.Output
 import io.ktor.utils.io.core.readBytes
 import io.ktor.utils.io.core.writeFully
+import kotlinx.serialization.ExperimentalSerializationApi
 import kotlinx.serialization.KSerializer
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.protobuf.ProtoBuf
@@ -26,6 +27,7 @@ import kotlin.reflect.KType
 
 public class JsonIOFormat<T : Any>(override val type: KType) : IOFormat<T> {
 
+    @Suppress("UNCHECKED_CAST")
     private val serializer: KSerializer<T> = serializer(type) as KSerializer<T>
 
     override fun readObject(input: Input): T = Json.decodeFromString(serializer, input.readUtf8String())
@@ -35,8 +37,10 @@ public class JsonIOFormat<T : Any>(override val type: KType) : IOFormat<T> {
     }
 }
 
+@OptIn(ExperimentalSerializationApi::class)
 public class ProtobufIOFormat<T : Any>(override val type: KType) : IOFormat<T> {
 
+    @Suppress("UNCHECKED_CAST")
     private val serializer: KSerializer<T> = serializer(type) as KSerializer<T>
 
     override fun readObject(input: Input): T = ProtoBuf.decodeFromByteArray(serializer, input.readBytes())
@@ -49,8 +53,7 @@ public class ProtobufIOFormat<T : Any>(override val type: KType) : IOFormat<T> {
 
 public class FileWorkspaceCache(public val cacheDirectory: Path) : WorkspaceCache {
 
-//    private fun <T : Any> TaskData<*>.checkType(taskType: KType): TaskData<T> = this as TaskData<T>
-
+    //    private fun <T : Any> TaskData<*>.checkType(taskType: KType): TaskData<T> = this as TaskData<T>
 
     @OptIn(DFExperimental::class, DFInternal::class)
     override suspend fun <T : Any> evaluate(result: TaskResult<T>): TaskResult<T> {
diff --git a/dataforge-workspace/src/commonMain/kotlin/space/kscience/dataforge/workspace/InMemoryWorkspaceCache.kt b/dataforge-workspace/src/jvmMain/kotlin/space/kscience/dataforge/workspace/InMemoryWorkspaceCache.kt
similarity index 83%
rename from dataforge-workspace/src/commonMain/kotlin/space/kscience/dataforge/workspace/InMemoryWorkspaceCache.kt
rename to dataforge-workspace/src/jvmMain/kotlin/space/kscience/dataforge/workspace/InMemoryWorkspaceCache.kt
index 53968c21..bb8ea9a4 100644
--- a/dataforge-workspace/src/commonMain/kotlin/space/kscience/dataforge/workspace/InMemoryWorkspaceCache.kt
+++ b/dataforge-workspace/src/jvmMain/kotlin/space/kscience/dataforge/workspace/InMemoryWorkspaceCache.kt
@@ -3,6 +3,7 @@ package space.kscience.dataforge.workspace
 import space.kscience.dataforge.meta.Meta
 import space.kscience.dataforge.names.Name
 import kotlin.reflect.KType
+import kotlin.reflect.full.isSubtypeOf
 
 private typealias TaskResultId = Pair<Name, Meta>
 
@@ -12,9 +13,10 @@ public class InMemoryWorkspaceCache : WorkspaceCache {
     // never do that at home!
     private val cache = HashMap<TaskResultId, HashMap<Name, TaskData<*>>>()
 
-    //TODO do actual check
-    @Suppress("UNUSED_PARAMETER")
-    private fun <T : Any> TaskData<*>.checkType(taskType: KType): TaskData<T> = this as TaskData<T>
+    @Suppress("UNCHECKED_CAST")
+    private fun <T : Any> TaskData<*>.checkType(taskType: KType): TaskData<T> =
+        if (type.isSubtypeOf(taskType)) this as TaskData<T>
+        else error("Cached data type mismatch: expected $taskType but got $type")
 
     override suspend fun <T : Any> evaluate(result: TaskResult<T>): TaskResult<T> {
         for (d: TaskData<T> in result) {
diff --git a/dataforge-workspace/src/jvmTest/kotlin/space/kscience/dataforge/workspace/FileWorkspaceCacheTest.kt b/dataforge-workspace/src/jvmTest/kotlin/space/kscience/dataforge/workspace/FileWorkspaceCacheTest.kt
index 9d427a76..00ca67cb 100644
--- a/dataforge-workspace/src/jvmTest/kotlin/space/kscience/dataforge/workspace/FileWorkspaceCacheTest.kt
+++ b/dataforge-workspace/src/jvmTest/kotlin/space/kscience/dataforge/workspace/FileWorkspaceCacheTest.kt
@@ -22,7 +22,8 @@ class FileWorkspaceCacheTest {
             }
             fileCache(Files.createTempDirectory("dataforge-temporary-cache"))
 
-            task<String> {
+            @Suppress("UNUSED_VARIABLE")
+            val echo by task<String> {
                 pipeFrom(dataByType<String>()) { arg, _, _ -> arg }
             }
         }