diff --git a/core/shared/src/main/scala/sigma/ast/SType.scala b/core/shared/src/main/scala/sigma/ast/SType.scala
index 7673c11de..b69a98834 100644
--- a/core/shared/src/main/scala/sigma/ast/SType.scala
+++ b/core/shared/src/main/scala/sigma/ast/SType.scala
@@ -102,14 +102,15 @@ object SType {
   /** Immutable empty IndexedSeq, can be used to avoid repeated allocations. */
   val EmptySeq: IndexedSeq[SType] = EmptyArray
 
+  // <= V5 types, see `allPredefTypes` scaladoc below
   private val v5PredefTypes = Array[SType](
       SBoolean, SByte, SShort, SInt, SLong, SBigInt, SContext,
       SGlobal, SHeader, SPreHeader, SAvlTree, SGroupElement, SSigmaProp, SString, SBox,
       SUnit, SAny)
 
+  // V6 types, see `allPredefTypes` scaladoc below
   private val v6PredefTypes = v5PredefTypes ++ Array(SUnsignedBigInt)
 
-
   /** All pre-defined types should be listed here. Note, NoType is not listed.
     * Should be in sync with sigmastate.lang.Types.predefTypes. */
   def allPredefTypes: Seq[SType] = {
@@ -147,6 +148,8 @@ object SType {
     * (SByte, SShort, SInt, SLong, SBigInt) and the generic tNum type parameter is
     * specialized accordingly.
     *
+    * Also, SUnsignedBigInt type is added in v6.0.
+    *
     * This difference in behaviour is tested by `property("MethodCall on numerics")`.
     *
     * The regression tests in `property("MethodCall Codes")` should pass.
@@ -487,7 +490,7 @@ case object SLong extends SPrimType with SEmbeddable with SNumericType with SMon
   }
 }
 
-/** Type of 256-bit  signed integer values. Implemented using [[java.math.BigInteger]]. */
+/** Type of 256-bit signed integer values. Implemented using [[java.math.BigInteger]]. */
 case object SBigInt extends SPrimType with SEmbeddable with SNumericType with SMonoType {
   override type WrappedType = BigInt
   override val typeCode: TypeCode = 6: Byte
diff --git a/core/shared/src/main/scala/sigma/util/Extensions.scala b/core/shared/src/main/scala/sigma/util/Extensions.scala
index 149d61f6c..5d1d9b7da 100644
--- a/core/shared/src/main/scala/sigma/util/Extensions.scala
+++ b/core/shared/src/main/scala/sigma/util/Extensions.scala
@@ -218,7 +218,6 @@ object Extensions {
     }
 
     @inline final def toUnsignedBigIntValueExact: BigInteger = {
-      // todo: make the check soft-forkable
       if (x.compareTo(BigInteger.ZERO) >= 0 && x.bitLength() <= 256) {
         x
       } else {
diff --git a/sc/shared/src/test/scala/sigmastate/utxo/BasicOpsSpecification.scala b/sc/shared/src/test/scala/sigmastate/utxo/BasicOpsSpecification.scala
index 07e5170af..7a5f6ae66 100644
--- a/sc/shared/src/test/scala/sigmastate/utxo/BasicOpsSpecification.scala
+++ b/sc/shared/src/test/scala/sigmastate/utxo/BasicOpsSpecification.scala
@@ -463,7 +463,8 @@ class BasicOpsSpecification extends CompilerTestingCommons
     }
   }
 
-  property("Bulletproof verification for a range proof") {
+  // todo: finish the range proof verification script and test
+  ignore("Bulletproof verification for a range proof") {
     /*
      * Original range proof verifier code by Benedikt Bunz:
      *