diff --git a/c_src/double-conversion/bignum.cc b/c_src/double-conversion/bignum.cc
index 747491a..3c88303 100644
--- a/c_src/double-conversion/bignum.cc
+++ b/c_src/double-conversion/bignum.cc
@@ -103,7 +103,7 @@ void Bignum::AssignDecimalString(Vector<const char> value) {
   const int kMaxUint64DecimalDigits = 19;
   Zero();
   int length = value.length();
-  int pos = 0;
+  unsigned int pos = 0;
   // Let's just say that each digit needs 4 bits.
   while (length >= kMaxUint64DecimalDigits) {
     uint64_t digits = ReadUInt64(value, pos, kMaxUint64DecimalDigits);