diff --git a/units/src/main/java/org/apache/tuweni/units/bigints/UInt256.java b/units/src/main/java/org/apache/tuweni/units/bigints/UInt256.java
index 4ade4ac..3a270d7 100644
--- a/units/src/main/java/org/apache/tuweni/units/bigints/UInt256.java
+++ b/units/src/main/java/org/apache/tuweni/units/bigints/UInt256.java
@@ -191,7 +191,7 @@
     result[INTS_SIZE - 2] = (int) (sum & LONG_MASK);
     constant &= result[INTS_SIZE - 2] == 0;
     long signExtent = (value >> 63) & LONG_MASK;
-    for (int i = INTS_SIZE - 2; i >= 0; --i) {
+    for (int i = INTS_SIZE - 3; i >= 0; --i) {
       sum = (this.ints[i] & LONG_MASK) + signExtent + (sum >>> 32);
       result[i] = (int) (sum & LONG_MASK);
       constant &= result[i] == 0;