diff --git a/constantine.nimble b/constantine.nimble
index 84b5964..06bb98b 100644
--- a/constantine.nimble
+++ b/constantine.nimble
@@ -17,7 +17,7 @@ proc test(fakeCurves: string, path: string, lang = "c") =
 ### tasks
 task test, "Run all tests":
   test "",                  "tests/test_primitives.nim"
-  test "",                  "tests/test_io.nim"
+  test "",                  "tests/test_io_bigints.nim"
   test "",                  "tests/test_bigints.nim"
   test "",                  "tests/test_bigints_multimod.nim"
   test "",                  "tests/test_bigints_vs_gmp.nim"
diff --git a/constantine/io/io_bigints.nim b/constantine/io/io_bigints.nim
index bf0be99..a1f48d5 100644
--- a/constantine/io/io_bigints.nim
+++ b/constantine/io/io_bigints.nim
@@ -273,7 +273,7 @@ func hexToPaddedByteArray(hexStr: string, output: var openArray[byte], order: st
   let maxStrSize = output.len * 2
   let size = hexStr.len - skip - nonBlanksCount
 
-  doAssert size <= maxStrSize
+  doAssert size <= maxStrSize, "size: " & $size & " (without blanks or prefix), maxSize: " & $maxStrSize
 
   if size < maxStrSize:
     # include extra byte if odd length
@@ -330,6 +330,7 @@ func fromHex*(T: type BigInt, s: string): T =
   # 1. Convert to canonical uint
   const canonLen = (T.bits + 8 - 1) div 8
   var bytes: array[canonLen, byte]
+  debugEcho "canonLen: ", canonLen
   hexToPaddedByteArray(s, bytes, littleEndian)
 
   # 2. Convert canonical uint to Big Int
diff --git a/tests/test_io.nim b/tests/test_io_bigints.nim
similarity index 100%
rename from tests/test_io.nim
rename to tests/test_io_bigints.nim