diff --git a/constantine.nimble b/constantine.nimble
index 29774f8..8efa80a 100644
--- a/constantine.nimble
+++ b/constantine.nimble
@@ -26,19 +26,26 @@ proc test(path: string) =
 task test, "Run all tests":
   # -d:testingCurves is configured in a *.nim.cfg for convenience
   test "tests/test_primitives.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"
+
+  test "tests/test_io_fields"
   test "tests/test_finite_fields.nim"
-  test "tests/test_finite_fields_vs_gmp.nim"
   test "tests/test_finite_fields_powinv.nim"
 
+  test "tests/test_bigints_vs_gmp.nim"
+  test "tests/test_finite_fields_vs_gmp.nim"
+
 task test_no_gmp, "Run tests that don't require GMP":
   # -d:testingCurves is configured in a *.nim.cfg for convenience
   test "tests/test_primitives.nim"
+
   test "tests/test_io_bigints.nim"
   test "tests/test_bigints.nim"
   test "tests/test_bigints_multimod.nim"
+
+  test "tests/test_io_fields"
   test "tests/test_finite_fields.nim"
   test "tests/test_finite_fields_powinv.nim"
diff --git a/constantine/arithmetic/bigints_raw.nim b/constantine/arithmetic/bigints_raw.nim
index 90e9060..130313a 100644
--- a/constantine/arithmetic/bigints_raw.nim
+++ b/constantine/arithmetic/bigints_raw.nim
@@ -662,7 +662,9 @@ func montyPowPrologue(
   # forcing this inline actually reduces the code size
 
   result.window = scratchspace.len.getWindowLen()
-  result.bigIntSize = a.numLimbs() * sizeof(Word) + sizeof(BigIntView.bitLength)
+  result.bigIntSize = a.numLimbs() * sizeof(Word) +
+                      offsetof(BigIntView, limbs) +
+                      sizeof(BigIntView.bitLength)
 
   # Precompute window content, special case for window = 1
   # (i.e scratchspace has only space for 2 temporaries)
@@ -671,12 +673,11 @@ func montyPowPrologue(
   if result.window == 1:
     copyMem(pointer scratchspace[1], pointer a, result.bigIntSize)
   else:
+    scratchspace[1].setBitLength(bitSizeof(M))
     copyMem(pointer scratchspace[2], pointer a, result.bigIntSize)
     for k in 2 ..< 1 shl result.window:
       scratchspace[k+1].montyMul(scratchspace[k], a, M, negInvModWord)
 
-    scratchspace[1].setBitLength(bitSizeof(M))
-
   # Set a to one
   copyMem(pointer a, pointer one, result.bigIntSize)
 
diff --git a/constantine/primitives/extended_precision.nim b/constantine/primitives/extended_precision.nim
index e7984df..297a4c5 100644
--- a/constantine/primitives/extended_precision.nim
+++ b/constantine/primitives/extended_precision.nim
@@ -123,8 +123,8 @@ when defined(gcc) or defined(clang) or defined(llvm_gcc):
                        " + (unsigned __int128)", a2," * (unsigned __int128)", b2,
                        " + (unsigned __int128)", c1,
                        " + (unsigned __int128)", c2, ";"].}
-      {.emit:[hi, " = (NU64)", dblPrec," >> ", 63'u64, ";"].}
-      {.emit:[lo, " = (NU64)", dblPrec," & ", 1'u64 shl 63 - 1, ";"].}
+      {.emit:[hi, " = (NU64)(", dblPrec," >> ", 63'u64, ");"].}
+      {.emit:[lo, " = (NU64)", dblPrec," & ", (1'u64 shl 63 - 1), ";"].}
 
 else:
   {.error: "Compiler not implemented".}
diff --git a/tests/test_finite_fields_powinv.nim b/tests/test_finite_fields_powinv.nim
index cddf2d2..122e87b 100644
--- a/tests/test_finite_fields_powinv.nim
+++ b/tests/test_finite_fields_powinv.nim
@@ -20,6 +20,25 @@ proc main() =
     test "n² mod 101":
       let exponent = BigInt[64].fromUint(2'u64)
 
+      block: # 1*1 mod 101
+        var n, expected: Fp[Fake101]
+
+        n.fromUint(1'u32)
+        expected = n
+
+        var r: Fp[Fake101]
+        r.prod(n, n)
+
+        var r_bytes: array[8, byte]
+        r_bytes.exportRawUint(r, cpuEndian)
+        let rU64 = cast[uint64](r_bytes)
+
+        check:
+          # Check equality in the Montgomery domain
+          bool(r == expected)
+          # Check equality when converting back to natural domain
+          1'u64 == rU64
+
       block: # 1^2 mod 101
         var n, expected: Fp[Fake101]
 
diff --git a/tests/test_io_fields.nim b/tests/test_io_fields.nim
index 5960a9b..1e06d7c 100644
--- a/tests/test_io_fields.nim
+++ b/tests/test_io_fields.nim
@@ -6,7 +6,7 @@
 #   * Apache v2 license (license terms in the root directory or at http://www.apache.org/licenses/LICENSE-2.0).
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
-import  unittest,
+import  unittest, random,
         ../constantine/io/[io_bigints, io_fields],
         ../constantine/config/curves,
         ../constantine/config/common,