diff --git a/AllTests-mainnet.md b/AllTests-mainnet.md
index 7960db9cc..52b1832ea 100644
--- a/AllTests-mainnet.md
+++ b/AllTests-mainnet.md
@@ -325,6 +325,8 @@ OK: 1/1 Fail: 0/1 Skip: 0/1
 + Overlong SSZ.decode: HashList[system.uint64, 32]                                           OK
 + Overlong SSZ.decode: List[system.uint64, 32]                                               OK
   Overlong SSZ.decode: Simple                                                                Skip
+  Overlong SSZ.decode: UInt128                                                               Skip
+  Overlong SSZ.decode: UInt256                                                               Skip
   Overlong SSZ.decode: array[0..31, byte]                                                    Skip
   Overlong SSZ.decode: bool                                                                  Skip
   Overlong SSZ.decode: limb_t                                                                Skip
@@ -337,6 +339,8 @@ OK: 1/1 Fail: 0/1 Skip: 0/1
 + Overlong readSszBytes: HashList[system.uint64, 32]                                         OK
 + Overlong readSszBytes: List[system.uint64, 32]                                             OK
   Overlong readSszBytes: Simple                                                              Skip
++ Overlong readSszBytes: UInt128                                                             OK
++ Overlong readSszBytes: UInt256                                                             OK
 + Overlong readSszBytes: array[0..31, byte]                                                  OK
 + Overlong readSszBytes: bool                                                                OK
 + Overlong readSszBytes: limb_t                                                              OK
@@ -349,6 +353,8 @@ OK: 1/1 Fail: 0/1 Skip: 0/1
 + Underlong SSZ.decode: HashList[system.uint64, 32]                                          OK
 + Underlong SSZ.decode: List[system.uint64, 32]                                              OK
 + Underlong SSZ.decode: Simple                                                               OK
++ Underlong SSZ.decode: UInt128                                                              OK
++ Underlong SSZ.decode: UInt256                                                              OK
 + Underlong SSZ.decode: array[0..31, byte]                                                   OK
 + Underlong SSZ.decode: bool                                                                 OK
 + Underlong SSZ.decode: limb_t                                                               OK
@@ -361,6 +367,8 @@ OK: 1/1 Fail: 0/1 Skip: 0/1
 + Underlong readSszBytes: HashList[system.uint64, 32]                                        OK
 + Underlong readSszBytes: List[system.uint64, 32]                                            OK
 + Underlong readSszBytes: Simple                                                             OK
++ Underlong readSszBytes: UInt128                                                            OK
++ Underlong readSszBytes: UInt256                                                            OK
 + Underlong readSszBytes: array[0..31, byte]                                                 OK
 + Underlong readSszBytes: bool                                                               OK
 + Underlong readSszBytes: limb_t                                                             OK
@@ -368,7 +376,7 @@ OK: 1/1 Fail: 0/1 Skip: 0/1
 + Underlong readSszBytes: uint32                                                             OK
 + Underlong readSszBytes: uint8                                                              OK
 ```
-OK: 36/48 Fail: 0/48 Skip: 12/48
+OK: 42/56 Fail: 0/56 Skip: 14/56
 
 ---TOTAL---
-OK: 201/213 Fail: 0/213 Skip: 12/213
+OK: 207/221 Fail: 0/221 Skip: 14/221
diff --git a/FixtureSSZGeneric-mainnet.md b/FixtureSSZGeneric-mainnet.md
index 18aff5308..aa0bdb1d7 100644
--- a/FixtureSSZGeneric-mainnet.md
+++ b/FixtureSSZGeneric-mainnet.md
@@ -2,8 +2,8 @@ FixtureSSZGeneric-mainnet
 ===
 ## Ethereum Foundation - SSZ generic types
 ```diff
-  Testing basic_vector inputs - invalid - skipping Vector[uint128, N] and Vector[uint256, N] Skip
-+ Testing basic_vector inputs - valid - skipping Vector[uint128, N] and Vector[uint256, N]   OK
+  Testing basic_vector inputs - invalid                                                      Skip
++ Testing basic_vector inputs - valid                                                        OK
 + Testing bitlist      inputs - invalid                                                      OK
 + Testing bitlist      inputs - valid                                                        OK
   Testing bitvector    inputs - invalid                                                      Skip
@@ -12,8 +12,8 @@ FixtureSSZGeneric-mainnet
 + Testing boolean      inputs - valid                                                        OK
 + Testing containers   inputs - invalid - skipping BitsStruct                                OK
 + Testing containers   inputs - valid - skipping BitsStruct                                  OK
-+ Testing uints        inputs - invalid - skipping uint128 and uint256                       OK
-+ Testing uints        inputs - valid - skipping uint128 and uint256                         OK
++ Testing uints        inputs - invalid                                                      OK
++ Testing uints        inputs - valid                                                        OK
 ```
 OK: 10/12 Fail: 0/12 Skip: 2/12
 
diff --git a/beacon_chain/spec/eth2_apis/eth2_rest_serialization.nim b/beacon_chain/spec/eth2_apis/eth2_rest_serialization.nim
index b03707561..46cc716a8 100644
--- a/beacon_chain/spec/eth2_apis/eth2_rest_serialization.nim
+++ b/beacon_chain/spec/eth2_apis/eth2_rest_serialization.nim
@@ -9,14 +9,13 @@ import stew/[results, base10, byteutils, endians2], presto/common,
        libp2p/peerid, serialization,
        json_serialization, json_serialization/std/[options, net],
        nimcrypto/utils as ncrutils
-import ".."/[forks, ssz_codec], ".."/datatypes/[phase0, altair, merge],
-       ".."/eth2_ssz_serialization,
-       ".."/".."/ssz/[ssz_serialization, codec, types],
+import ".."/[eth2_ssz_serialization, forks],
+       ".."/datatypes/[phase0, altair, merge],
        "."/rest_types
 
 export
   results, peerid, common, serialization, json_serialization, options, net,
-  rest_types, ssz_codec, ssz_serialization, codec, types
+  eth2_ssz_serialization, rest_types
 
 Json.createFlavor RestJson
 
diff --git a/beacon_chain/ssz/merkleization.nim b/beacon_chain/ssz/merkleization.nim
index 141a75ed5..c9e97691c 100644
--- a/beacon_chain/ssz/merkleization.nim
+++ b/beacon_chain/ssz/merkleization.nim
@@ -413,7 +413,7 @@ template merkleizeFields(totalElements: static Limit, body: untyped): Eth2Digest
   getFinalHash(merkleizer)
 
 template writeBytesLE(chunk: var array[bytesPerChunk, byte], atParam: int,
-                      val: SomeUnsignedInt) =
+                      val: UintN) =
   let at = atParam
   chunk[at ..< at + sizeof(val)] = toBytesLE(val)
 
@@ -528,7 +528,7 @@ func maxChunksCount(T: type, maxLen: Limit): Limit =
 func hashTreeRootAux[T](x: T): Eth2Digest =
   when T is bool|char:
     result.data[0] = byte(x)
-  elif T is SomeUnsignedInt:
+  elif T is UintN:
     when cpuEndian == bigEndian:
       result.data[0..<sizeof(x)] = toBytesLE(x)
     else:
diff --git a/beacon_chain/ssz/types.nim b/beacon_chain/ssz/types.nim
index 8ee4fe212..e454504f1 100644
--- a/beacon_chain/ssz/types.nim
+++ b/beacon_chain/ssz/types.nim
@@ -9,20 +9,20 @@
 
 import
   std/[tables, typetraits, strformat],
-  stew/shims/macros, stew/[byteutils, bitops2, objects],
+  stew/shims/macros, stew/[byteutils, bitops2, objects], stint,
   serialization/[object_serialization, errors],
   json_serialization,
   "."/[bitseqs],
   ../spec/digest
 
-export bitseqs, json_serialization
+export stint, bitseqs, json_serialization
 
 const
   offsetSize* = 4
   bytesPerChunk* = 32
 
 type
-  UintN* = SomeUnsignedInt
+  UintN* = SomeUnsignedInt|UInt128|UInt256
   BasicType* = bool|UintN
 
   Limit* = int64
diff --git a/tests/official/test_fixture_ssz_generic_types.nim b/tests/official/test_fixture_ssz_generic_types.nim
index 48b58a338..564de364e 100644
--- a/tests/official/test_fixture_ssz_generic_types.nim
+++ b/tests/official/test_fixture_ssz_generic_types.nim
@@ -10,7 +10,7 @@ import
   os, strutils, streams, strformat, strscans,
   macros, typetraits,
   # Status libraries
-  faststreams, snappy, ../testutil,
+  faststreams, snappy, stint, ../testutil,
   # Third-party
   yaml,
   # Beacon chain internals
@@ -101,7 +101,7 @@ macro testVector(typeIdent: string, size: int): untyped =
   # sizes: 1, 2, 3, 4, 5, 8, 16, 31, 512, 513
   #
   # We allocate in a ref array to not run out of stack space
-  let types = ["bool", "uint8", "uint16", "uint32", "uint64"] # "uint128", "uint256"]
+  let types = ["bool", "uint8", "uint16", "uint32", "uint64", "uint128", "uint256"]
   let sizes = [1, 2, 3, 4, 5, 8, 16, 31, 512, 513]
 
   var dispatcher = nnkIfStmt.newTree()
@@ -111,7 +111,11 @@ macro testVector(typeIdent: string, size: int): untyped =
     for s in sizes:
       # if size == s // elif size == s
       let T = nnkBracketExpr.newTree(
-        ident"array", newLit(s), ident(t)
+        ident"array", newLit(s),
+        case t
+        of "uint128": ident("UInt128")
+        of "uint256": ident("UInt256")
+        else: ident(t)
       )
       var testStmt = quote do:
         checkBasic(`T`, dir, expectedHash)
@@ -128,11 +132,9 @@ macro testVector(typeIdent: string, size: int): untyped =
       sizeDispatch
     )
   dispatcher.add nnkElse.newTree quote do:
-    # TODO: support uint128 and uint256
-    if `typeIdent` != "uint128" and `typeIdent` != "uint256":
-      raise newException(ValueError,
-        "Unsupported **type** in type/size combination: array[" &
-        $`size` & ", " & `typeIdent` & ']')
+    raise newException(ValueError,
+      "Unsupported **type** in type/size combination: array[" &
+      $`size` & ", " & `typeIdent` & ']')
 
   result = dispatcher
   # echo result.toStrLit() # view the generated code
@@ -204,16 +206,12 @@ proc sszCheck(baseDir, sszType, sszSubType: string) =
     let wasMatched = scanf(sszSubType, "uint_$i", bitsize)
     doAssert wasMatched
     case bitsize
-    of 8:  checkBasic(uint8, dir, expectedHash)
-    of 16: checkBasic(uint16, dir, expectedHash)
-    of 32: checkBasic(uint32, dir, expectedHash)
-    of 64: checkBasic(uint64, dir, expectedHash)
-    of 128:
-      # Compile-time issues
-      discard # checkBasic(Stuint[128], dir, expectedHash)
-    of 256:
-      # Compile-time issues
-      discard # checkBasic(Stuint[256], dir, expectedHash)
+    of 8:   checkBasic(uint8, dir, expectedHash)
+    of 16:  checkBasic(uint16, dir, expectedHash)
+    of 32:  checkBasic(uint32, dir, expectedHash)
+    of 64:  checkBasic(uint64, dir, expectedHash)
+    of 128: checkBasic(UInt128, dir, expectedHash)
+    of 256: checkBasic(UInt256, dir, expectedHash)
     else:
       raise newException(ValueError, "unknown uint in test: " & sszSubType)
   of "basic_vector": checkVector(sszSubType, dir, expectedHash)
@@ -252,10 +250,6 @@ suite "Ethereum Foundation - SSZ generic types":
 
     var skipped: string
     case sszType
-    of "uints":
-      skipped = " - skipping uint128 and uint256"
-    of "basic_vector":
-      skipped = " - skipping Vector[uint128, N] and Vector[uint256, N]"
     of "containers":
       skipped = " - skipping BitsStruct"
 
diff --git a/tests/ssz/test_ssz_serialization.nim b/tests/ssz/test_ssz_serialization.nim
index 2e1a7f453..f65bcfede 100644
--- a/tests/ssz/test_ssz_serialization.nim
+++ b/tests/ssz/test_ssz_serialization.nim
@@ -343,6 +343,8 @@ suite "underlong values":
   testit(default(uint16))
   testit(default(uint32))
   testit(default(uint64))
+  testit(default(UInt128))
+  testit(default(UInt256))
   testit(default(array[32, uint8]))
   testit(default(HashArray[32, uint8]))
   testit(List[uint64, 32].init(@[42'u64]))