diff --git a/libevmcore/Assembly.cpp b/libevmcore/Assembly.cpp
index f7a71102f..889865d9f 100644
--- a/libevmcore/Assembly.cpp
+++ b/libevmcore/Assembly.cpp
@@ -291,7 +291,7 @@ Assembly& Assembly::optimise(bool _enable)
 		{ Instruction::SDIV, [](u256 a, u256 b)->u256{return s2u(u2s(a) / u2s(b));} },
 		{ Instruction::MOD, [](u256 a, u256 b)->u256{return a % b;} },
 		{ Instruction::SMOD, [](u256 a, u256 b)->u256{return s2u(u2s(a) % u2s(b));} },
-		{ Instruction::EXP, [](u256 a, u256 b)->u256{return (u256)boost::multiprecision::powm((bigint)a, (bigint)b, bigint(2) << 256);} },
+		{ Instruction::EXP, [](u256 a, u256 b)->u256{return (u256)boost::multiprecision::powm((bigint)a, (bigint)b, bigint(1) << 256);} },
 		{ Instruction::SIGNEXTEND, signextend },
 		{ Instruction::LT, [](u256 a, u256 b)->u256{return a < b ? 1 : 0;} },
 		{ Instruction::GT, [](u256 a, u256 b)->u256{return a > b ? 1 : 0;} },