diff --git a/unix/types_darwin.go b/unix/types_darwin.go
index 1764b312..71ada9e1 100644
--- a/unix/types_darwin.go
+++ b/unix/types_darwin.go
@@ -178,6 +178,7 @@ const (
 	SizeofSockaddrDatalink = C.sizeof_struct_sockaddr_dl
 	SizeofSockaddrCtl      = C.sizeof_struct_sockaddr_ctl
 	SizeofLinger           = C.sizeof_struct_linger
+	SizeofIovec            = C.sizeof_struct_iovec
 	SizeofIPMreq           = C.sizeof_struct_ip_mreq
 	SizeofIPv6Mreq         = C.sizeof_struct_ipv6_mreq
 	SizeofMsghdr           = C.sizeof_struct_msghdr
diff --git a/unix/ztypes_darwin_386.go b/unix/ztypes_darwin_386.go
index 830fbb35..725b4bee 100644
--- a/unix/ztypes_darwin_386.go
+++ b/unix/ztypes_darwin_386.go
@@ -269,6 +269,7 @@ const (
 	SizeofSockaddrDatalink = 0x14
 	SizeofSockaddrCtl      = 0x20
 	SizeofLinger           = 0x8
+	SizeofIovec            = 0x8
 	SizeofIPMreq           = 0x8
 	SizeofIPv6Mreq         = 0x14
 	SizeofMsghdr           = 0x1c
diff --git a/unix/ztypes_darwin_amd64.go b/unix/ztypes_darwin_amd64.go
index e53a7c49..080ffce3 100644
--- a/unix/ztypes_darwin_amd64.go
+++ b/unix/ztypes_darwin_amd64.go
@@ -274,6 +274,7 @@ const (
 	SizeofSockaddrDatalink = 0x14
 	SizeofSockaddrCtl      = 0x20
 	SizeofLinger           = 0x8
+	SizeofIovec            = 0x10
 	SizeofIPMreq           = 0x8
 	SizeofIPv6Mreq         = 0x14
 	SizeofMsghdr           = 0x30
diff --git a/unix/ztypes_darwin_arm.go b/unix/ztypes_darwin_arm.go
index 98be973e..f2a77bc4 100644
--- a/unix/ztypes_darwin_arm.go
+++ b/unix/ztypes_darwin_arm.go
@@ -269,6 +269,7 @@ const (
 	SizeofSockaddrDatalink = 0x14
 	SizeofSockaddrCtl      = 0x20
 	SizeofLinger           = 0x8
+	SizeofIovec            = 0x8
 	SizeofIPMreq           = 0x8
 	SizeofIPv6Mreq         = 0x14
 	SizeofMsghdr           = 0x1c
diff --git a/unix/ztypes_darwin_arm64.go b/unix/ztypes_darwin_arm64.go
index ddae5afe..c9492428 100644
--- a/unix/ztypes_darwin_arm64.go
+++ b/unix/ztypes_darwin_arm64.go
@@ -274,6 +274,7 @@ const (
 	SizeofSockaddrDatalink = 0x14
 	SizeofSockaddrCtl      = 0x20
 	SizeofLinger           = 0x8
+	SizeofIovec            = 0x10
 	SizeofIPMreq           = 0x8
 	SizeofIPv6Mreq         = 0x14
 	SizeofMsghdr           = 0x30