diff --git a/api/except.txt b/api/except.txt
index 857ebb5d7d..fbabd18a81 100644
--- a/api/except.txt
+++ b/api/except.txt
@@ -1,4 +1,5 @@
 pkg encoding/json, method (*RawMessage) MarshalJSON() ([]uint8, error)
+pkg math/big, type Word uintptr
 pkg net, func ListenUnixgram(string, *UnixAddr) (*UDPConn, error)
 pkg os (linux-arm), const O_SYNC = 4096
 pkg os (linux-arm-cgo), const O_SYNC = 4096
diff --git a/src/math/big/arith.go b/src/math/big/arith.go
index d7ea8381e7..1101451f98 100644
--- a/src/math/big/arith.go
+++ b/src/math/big/arith.go
@@ -9,7 +9,7 @@
 package big
 
 // A Word represents a single digit of a multi-precision unsigned integer.
-type Word uintptr
+type Word uint
 
 const (
 	// Compute the size _S of a Word in bytes.