diff --git a/docs/assembly.rst b/docs/assembly.rst
index 855f5d721..4e665b7ec 100644
--- a/docs/assembly.rst
+++ b/docs/assembly.rst
@@ -92,7 +92,7 @@ you really know what you are doing.
         function sumAsm(uint[] _data) returns (uint o_sum) {
             for (uint i = 0; i < _data.length; ++i) {
                 assembly {
-                    o_sum := mload(add(add(_data, 0x20), mul(i, 0x20)))
+                    o_sum := add(o_sum, mload(add(add(_data, 0x20), mul(i, 0x20))))
                 }
             }
         }