diff --git a/ergo-core/src/test/scala/org/ergoplatform/utils/generators/ErgoCoreGenerators.scala b/ergo-core/src/test/scala/org/ergoplatform/utils/generators/ErgoCoreGenerators.scala
index e56f87641b..0cbb42425e 100644
--- a/ergo-core/src/test/scala/org/ergoplatform/utils/generators/ErgoCoreGenerators.scala
+++ b/ergo-core/src/test/scala/org/ergoplatform/utils/generators/ErgoCoreGenerators.scala
@@ -88,11 +88,37 @@ object ErgoCoreGenerators {
       scorex.util.Random.randomBytes
     }
 
+  /**
+   * Main KV generator: contains special handling for key.head == 0
+   */
   def extensionKvGen(keySize: Int, valuesSize: Int): Gen[(Array[Byte], Array[Byte])] = for {
     key <- genSecureBoundedBytes(keySize, keySize)
     value <- if (key.head == 0) genSecureBoundedBytes(4, 4) else genSecureBoundedBytes(valuesSize, valuesSize)
   } yield (key, value)
 
+  /**
+   * Random KV generator: all random key/values
+   */
+  def extensionKvGenImvValue(keySize: Int, valuesSize: Int): Gen[(Array[Byte], Array[Byte])] = for {
+    key <- genSecureBoundedBytes(keySize, keySize)
+    value <- genSecureBoundedBytes(valuesSize, valuesSize)
+  } yield (key, value)
+
+  /**
+   * Special KV generator: does not generate key.head == 1, because improperly packed interlink
+   * would be generated, leading to failure.
+   */
+  def extensionKvGenValidMKV(keySize: Int, valueSize: Int): Gen[(Array[Byte], Array[Byte])] = {
+    def keyGenHeadNotOne: Gen[Array[Byte]] = genSecureBoundedBytes(keySize, keySize).flatMap { key =>
+      if (key.headOption.contains(1.toByte)) keyGenHeadNotOne else Gen.const(key)
+    }
+
+    for {
+      key <- keyGenHeadNotOne
+      value <- genSecureBoundedBytes(valueSize, valueSize)
+    } yield (key, value)
+  }
+
   lazy val extensionGen: Gen[Extension] = for {
     headerId <- modifierIdGen
     mandatoryElements <- Gen.mapOf(extensionKvGen(Extension.FieldKeySize, Extension.FieldValueMaxSize))
diff --git a/src/test/scala/org/ergoplatform/nodeView/state/ErgoStateContextSpec.scala b/src/test/scala/org/ergoplatform/nodeView/state/ErgoStateContextSpec.scala
index 386c831b8b..92ef1e4580 100644
--- a/src/test/scala/org/ergoplatform/nodeView/state/ErgoStateContextSpec.scala
+++ b/src/test/scala/org/ergoplatform/nodeView/state/ErgoStateContextSpec.scala
@@ -67,7 +67,7 @@ class ErgoStateContextSpec extends ErgoCorePropertyTest {
     sc.appendFullBlock(fbWithFields(imvKey +: oldFields)) shouldBe 'failure
 
     // validation of field value sizes
-    val imvValue = extensionKvGen(Extension.FieldKeySize, Extension.FieldValueMaxSize + 1).sample.get
+    val imvValue = extensionKvGenImvValue(Extension.FieldKeySize, Extension.FieldValueMaxSize + 1).sample.get
     sc.appendFullBlock(fbWithFields(imvValue +: oldFields)) shouldBe 'failure
 
     // validation of incorrect interlinks
@@ -76,8 +76,8 @@ class ErgoStateContextSpec extends ErgoCorePropertyTest {
     ).fields
     sc.appendFullBlock(fbWithFields(invalidInterlinks ++ oldFields)) shouldBe 'failure
 
+    val validMKV = extensionKvGenValidMKV(Extension.FieldKeySize, Extension.FieldValueMaxSize).sample.get
     // validation of key duplicates in fields
-    val validMKV = extensionKvGen(Extension.FieldKeySize, Extension.FieldValueMaxSize).sample.get
     sc.appendFullBlock(fbWithFields(Seq(validMKV, validMKV) ++ oldFields)) shouldBe 'failure
 
     // valid application of correct extension