diff --git a/bignum/src/commonMain/kotlin/com/ionspin/kotlin/bignum/integer/BigInteger.kt b/bignum/src/commonMain/kotlin/com/ionspin/kotlin/bignum/integer/BigInteger.kt
index 05ee6473..24eb9843 100644
--- a/bignum/src/commonMain/kotlin/com/ionspin/kotlin/bignum/integer/BigInteger.kt
+++ b/bignum/src/commonMain/kotlin/com/ionspin/kotlin/bignum/integer/BigInteger.kt
@@ -635,8 +635,15 @@ class BigInteger internal constructor(wordArray: WordArray, requestedSign: Sign)
         return BigInteger(arithmetic.and(this.magnitude, other.magnitude), sign)
     }
 
+    /** Returns a new BigInt with bits combining [this], [other] doing a bitwise `|`/`or` operation. Forces sign to positive. */
+    // TODO Investigate what is expected behavior when one of the operand is negative. Is it considered to be two's complement?
     override infix fun or(other: BigInteger): BigInteger {
-        return BigInteger(arithmetic.or(this.magnitude, other.magnitude), sign)
+        val resultMagnitude = arithmetic.or(this.magnitude, other.magnitude)
+        val resultSign = when {
+            isResultZero(resultMagnitude) -> Sign.ZERO
+            else -> Sign.POSITIVE
+        }
+        return BigInteger(resultMagnitude, resultSign)
     }
 
     override infix fun xor(other: BigInteger): BigInteger {
diff --git a/bignum/src/commonMain/kotlin/com/ionspin/kotlin/bignum/integer/base63/array/BigInteger63Arithmetic.kt b/bignum/src/commonMain/kotlin/com/ionspin/kotlin/bignum/integer/base63/array/BigInteger63Arithmetic.kt
index 397710f0..450c39b9 100644
--- a/bignum/src/commonMain/kotlin/com/ionspin/kotlin/bignum/integer/base63/array/BigInteger63Arithmetic.kt
+++ b/bignum/src/commonMain/kotlin/com/ionspin/kotlin/bignum/integer/base63/array/BigInteger63Arithmetic.kt
@@ -1972,6 +1972,7 @@ internal object BigInteger63Arithmetic : BigIntegerArithmetic {
     }
 
     override fun or(operand: ULongArray, mask: ULongArray): ULongArray {
+        if (operand.size < mask.size) return or(mask, operand)
         return removeLeadingZeros(
             ULongArray(operand.size) {
                 if (it < mask.size) {
diff --git a/bignum/src/commonTest/kotlin/com/ionspin/kotlin/bignum/integer/integer/BigIntegerBitwiseOperations.kt b/bignum/src/commonTest/kotlin/com/ionspin/kotlin/bignum/integer/integer/BigIntegerBitwiseOperations.kt
index 5c70ceff..c3603b49 100644
--- a/bignum/src/commonTest/kotlin/com/ionspin/kotlin/bignum/integer/integer/BigIntegerBitwiseOperations.kt
+++ b/bignum/src/commonTest/kotlin/com/ionspin/kotlin/bignum/integer/integer/BigIntegerBitwiseOperations.kt
@@ -27,6 +27,42 @@ import kotlin.test.assertEquals
  * on 01-Nov-2019
  */
 class BigIntegerBitwiseOperations {
+    @Test
+    fun andWithZero() {
+        val operand = BigInteger.parseString("11110000", 2)
+        val mask = BigInteger.ZERO
+
+        assertEquals(mask, operand and mask)
+        assertEquals(mask, mask and operand)
+    }
+
+    @Test
+    fun andBiggerThanLongMaxWithZero() {
+        val operand = BigInteger.parseString("9223372036854775808", 10)
+        val mask = BigInteger.ZERO
+
+        assertEquals(mask, operand and mask)
+        assertEquals(mask, mask and operand)
+    }
+
+    @Test
+    fun orWithZero() {
+        val operand = BigInteger.parseString("11110000", 2)
+        val mask = BigInteger.ZERO
+
+        assertEquals(operand, operand or mask)
+        assertEquals(operand, mask or operand)
+    }
+
+    @Test
+    fun orBiggerThanLongMaxWithZero() {
+        val operand = BigInteger.parseString("9223372036854775808", 10)
+        val mask = BigInteger.ZERO
+
+        assertEquals(operand, operand or mask)
+        assertEquals(operand, mask or operand)
+    }
+
     @Test
     fun xorWithZero() {
         val operand = BigInteger.parseString("11110000", 2)
@@ -34,10 +70,8 @@ class BigIntegerBitwiseOperations {
         val xorResult = operand xor mask
         println("Xor result: ${xorResult.toString(2)}")
 
-        val expectedResult = operand
-
-        assertEquals(expectedResult, xorResult)
-        assertEquals(expectedResult, mask xor operand)
+        assertEquals(operand, xorResult)
+        assertEquals(operand, mask xor operand)
     }
 
     @Test
@@ -45,9 +79,7 @@ class BigIntegerBitwiseOperations {
         val operand = BigInteger.parseString("9223372036854775808", 10)
         val mask = BigInteger.ZERO
 
-        val expectedResult = operand
-
-        assertEquals(expectedResult, operand xor mask)
-        assertEquals(expectedResult, mask xor operand)
+        assertEquals(operand, operand xor mask)
+        assertEquals(operand, mask xor operand)
     }
 }