diff --git a/platform/workspaceModel/codegen-impl/src/main/kotlin/com/intellij/workspaceModel/codegen/engine/impl/CodeGeneratorImpl.kt b/platform/workspaceModel/codegen-impl/src/main/kotlin/com/intellij/workspaceModel/codegen/engine/impl/CodeGeneratorImpl.kt
index 840b4d4be84a..81eaede4ea30 100644
--- a/platform/workspaceModel/codegen-impl/src/main/kotlin/com/intellij/workspaceModel/codegen/engine/impl/CodeGeneratorImpl.kt
+++ b/platform/workspaceModel/codegen-impl/src/main/kotlin/com/intellij/workspaceModel/codegen/engine/impl/CodeGeneratorImpl.kt
@@ -6,15 +6,14 @@ import com.intellij.workspaceModel.codegen.engine.CodeGenerator
 import com.intellij.workspaceModel.codegen.engine.GeneratedCode
 import com.intellij.workspaceModel.codegen.engine.GenerationProblem
 import com.intellij.workspaceModel.codegen.engine.GenerationResult
-import com.intellij.workspaceModel.codegen.writer.generateBuilderCode
-import com.intellij.workspaceModel.codegen.writer.generateCompanionObject
-import com.intellij.workspaceModel.codegen.writer.generateExtensionCode
-import com.intellij.workspaceModel.codegen.writer.implWsCode
+import com.intellij.workspaceModel.codegen.writer.*
 
 class CodeGeneratorImpl : CodeGenerator {
   override fun generate(module: CompiledObjModule): GenerationResult {
     val problems = ArrayList<GenerationProblem>()
     val reporter = ProblemReporter { problems.add(it) }
+
+    checkExtensionFields(module, reporter)
     val objClassToBuilderInterface = module.types.associateWith {
       val builderInterface = it.generateBuilderCode(reporter)
       builderInterface
diff --git a/platform/workspaceModel/codegen-impl/src/main/kotlin/com/intellij/workspaceModel/codegen/writer/moduleChecker.kt b/platform/workspaceModel/codegen-impl/src/main/kotlin/com/intellij/workspaceModel/codegen/writer/moduleChecker.kt
new file mode 100644
index 000000000000..5e7b9416061b
--- /dev/null
+++ b/platform/workspaceModel/codegen-impl/src/main/kotlin/com/intellij/workspaceModel/codegen/writer/moduleChecker.kt
@@ -0,0 +1,16 @@
+// Copyright 2000-2023 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+package com.intellij.workspaceModel.codegen.writer
+
+import com.intellij.workspaceModel.codegen.deft.meta.CompiledObjModule
+import com.intellij.workspaceModel.codegen.engine.GenerationProblem
+import com.intellij.workspaceModel.codegen.engine.ProblemLocation
+import com.intellij.workspaceModel.codegen.engine.impl.ProblemReporter
+
+internal fun checkExtensionFields(module: CompiledObjModule, reporter: ProblemReporter) {
+  module.extensions.forEach { extProperty ->
+    if (!extProperty.valueType.isRefType()) {
+      reporter.reportProblem(GenerationProblem("Extension property is supposed to be a reference to another entity only.",
+                                               GenerationProblem.Level.ERROR, ProblemLocation.Property(extProperty)))
+    }
+  }
+}
diff --git a/platform/workspaceModel/codegen-impl/src/main/kotlin/com/intellij/workspaceModel/codegen/writer/refsUtilExtensions.kt b/platform/workspaceModel/codegen-impl/src/main/kotlin/com/intellij/workspaceModel/codegen/writer/refsUtilExtensions.kt
index b34136ce76d3..86139e1aa239 100644
--- a/platform/workspaceModel/codegen-impl/src/main/kotlin/com/intellij/workspaceModel/codegen/writer/refsUtilExtensions.kt
+++ b/platform/workspaceModel/codegen-impl/src/main/kotlin/com/intellij/workspaceModel/codegen/writer/refsUtilExtensions.kt
@@ -3,6 +3,7 @@ package com.intellij.workspaceModel.codegen.writer
 import com.intellij.workspaceModel.codegen.deft.meta.ObjClass
 import com.intellij.workspaceModel.codegen.deft.meta.OwnProperty
 import com.intellij.workspaceModel.codegen.deft.meta.ValueType
+import com.intellij.workspaceModel.codegen.writer.fields.javaType
 import com.intellij.workspaceModel.storage.url.VirtualFileUrl
 
 val ObjClass<*>.refsFields: List<OwnProperty<*, *>>
@@ -18,7 +19,7 @@ fun ValueType<*>.getRefType(): ValueType.ObjRef<*> = when (this) {
   is ValueType.ObjRef<*> -> this
   is ValueType.Optional<*> -> type.getRefType()
   is ValueType.Collection<*, *> -> elementType.getRefType()
-  else -> error("Unsupported type of requester, should be called only if `isRefType` is true")
+  else -> error("${this.javaType} isn't a reference type. The method has to be called only for the reference type of fields")
 }
 
 fun ValueType<*>.isRefType(): Boolean = when (this) {