diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e11343b..a80346a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -22,7 +22,7 @@ jobs:
             cpu: amd64
           #- os: windows
             #cpu: i386
-        branch: [version-1-2, version-1-4, version-1-6, devel]
+        branch: [version-1-6, devel]
         include:
           - target:
               os: linux
@@ -43,7 +43,7 @@ jobs:
 
     name: '${{ matrix.target.os }}-${{ matrix.target.cpu }} (Nim ${{ matrix.branch }})'
     runs-on: ${{ matrix.builder }}
-    continue-on-error: ${{ matrix.branch == 'version-1-6' || matrix.branch == 'devel' }}
+    continue-on-error: ${{ matrix.branch == 'devel' }}
     timeout-minutes: 60
     steps:
       - name: Checkout
diff --git a/eth.nimble b/eth.nimble
index 6121262..0034181 100644
--- a/eth.nimble
+++ b/eth.nimble
@@ -4,7 +4,7 @@ description   = "Ethereum Common library"
 license       = "MIT"
 skipDirs      = @["tests"]
 
-requires "nim >= 1.2.0",
+requires "nim >= 1.6.0",
          "nimcrypto",
          "stint",
          "secp256k1",
@@ -18,17 +18,11 @@ requires "nim >= 1.2.0",
          "testutils",
          "unittest2"
 
-let styleCheckStyle =
-  if (NimMajor, NimMinor) < (1, 6):
-    "hint"
-  else:
-    "error"
-
 let commonParams =
   " --skipUserCfg:on" &
   " --verbosity:0 --hints:off" &
-  " --warning[ObservableStores]:off " &
-  " --styleCheck:usages --styleCheck:" & styleCheckStyle &
+  " --warning[ObservableStores]:off" &
+  " --styleCheck:usages --styleCheck:error" &
   " " & getEnv("NIMFLAGS") &
   " -d:chronosStrictException" &
   " -d:chronicles_log_level=TRACE"
diff --git a/eth/common/eth_hash.nim b/eth/common/eth_hash.nim
index f4fbb3f..eb0de80 100644
--- a/eth/common/eth_hash.nim
+++ b/eth/common/eth_hash.nim
@@ -1,13 +1,10 @@
-# Copyright (c) 2022 Status Research & Development GmbH
+# Copyright (c) 2022-2023 Status Research & Development GmbH
 # Licensed and distributed under either of
 #   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
 #   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
-when (NimMajor, NimMinor) < (1, 4):
-  {.push raises: [Defect].}
-else:
-  {.push raises: [].}
+{.push raises: [].}
 
 ## keccak256 is used across ethereum as the "default" hash function and this
 ## module provides a type and some helpers to produce such hashes
diff --git a/eth/common/eth_types.nim b/eth/common/eth_types.nim
index 38285d4..21d17ce 100644
--- a/eth/common/eth_types.nim
+++ b/eth/common/eth_types.nim
@@ -1,15 +1,12 @@
-# Copyright (c) 2022 Status Research & Development GmbH
+# Copyright (c) 2022-2023 Status Research & Development GmbH
 # Licensed and distributed under either of
 #   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
 #   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
-when (NimMajor, NimMinor) < (1, 4):
-  {.push raises: [Defect].}
-else:
-  {.push raises: [].}
+{.push raises: [].}
 
-## Core ethereum types and smalll helpers - keep focused as it gets imported
+## Core ethereum types and small helpers - keep focused as it gets imported
 ## from many places
 
 import
diff --git a/eth/db/kvstore.nim b/eth/db/kvstore.nim
index 3b54d37..653fc4b 100644
--- a/eth/db/kvstore.nim
+++ b/eth/db/kvstore.nim
@@ -1,5 +1,5 @@
 # beacon_chain
-# Copyright (c) 2018-2020 Status Research & Development GmbH
+# Copyright (c) 2018-2023 Status Research & Development GmbH
 # Licensed and distributed under either of
 #   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
 #   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
@@ -8,12 +8,8 @@
 ## Simple Key-Value store database interface that allows creating multiple
 ## tables within each store
 
-when (NimMajor, NimMinor) < (1, 4):
-  {.push raises: [Defect].}
-  {.pragma: callback, gcsafe, raises: [Defect].}
-else:
-  {.push raises: [].}
-  {.pragma: callback, gcsafe, raises: [].}
+{.push raises: [].}
+{.pragma: callback, gcsafe, raises: [].}
 
 import
   std/[tables, hashes, sets],
diff --git a/eth/db/kvstore_sqlite3.nim b/eth/db/kvstore_sqlite3.nim
index 6b13455..f240777 100644
--- a/eth/db/kvstore_sqlite3.nim
+++ b/eth/db/kvstore_sqlite3.nim
@@ -1,11 +1,7 @@
 ## Implementation of KvStore based on sqlite3
 
-when (NimMajor, NimMinor) < (1, 4):
-  {.push raises: [Defect].}
-  {.pragma: callback, gcsafe, raises: [Defect].}
-else:
-  {.push raises: [Defect].}
-  {.pragma: callback, gcsafe, raises: [].}
+{.push raises: [Defect].}
+{.pragma: callback, gcsafe, raises: [].}
 
 import
   std/[os, options, strformat, typetraits],
diff --git a/eth/trie/hexary.nim b/eth/trie/hexary.nim
index c262363..dcda646 100644
--- a/eth/trie/hexary.nim
+++ b/eth/trie/hexary.nim
@@ -32,9 +32,6 @@ proc expectHash(r: Rlp): seq[byte] =
     raise newException(RlpTypeMismatch,
       "RLP expected to be a Keccak hash value, but has an incorrect length")
 
-when (NimMajor, NimMinor, NimPatch) < (1, 4, 0):
-  type AssertionDefect = AssertionError
-
 type MissingNodeError* = ref object of AssertionDefect
   path*: NibblesSeq
   nodeHashBytes*: seq[byte]
diff --git a/tests/rlp/test_api_usage.nim b/tests/rlp/test_api_usage.nim
index e9578f2..0ca6ee0 100644
--- a/tests/rlp/test_api_usage.nim
+++ b/tests/rlp/test_api_usage.nim
@@ -35,10 +35,6 @@ proc test_blockBodyTranscode() =
   for n in 0 ..< min(trBlkSeq.len, trBlkSeq.len):
     check (n, trBlkSeq[n]) == (n, blkSeq[n])
 
-
-when (NimMajor, NimMinor, NimPatch) < (1, 4, 0):
-  type AssertionDefect = AssertionError
-
 suite "test api usage":
   test "empty bytes are not a proper RLP":
     var rlp = rlpFromBytes seq[byte](@[])