diff --git a/curve25519/internal/field/_asm/fe_amd64_asm.go b/curve25519/internal/field/_asm/fe_amd64_asm.go
index 535d9ae..1f36529 100644
--- a/curve25519/internal/field/_asm/fe_amd64_asm.go
+++ b/curve25519/internal/field/_asm/fe_amd64_asm.go
@@ -11,13 +11,16 @@ import (
 	. "github.com/mmcloughlin/avo/gotypes"
 	. "github.com/mmcloughlin/avo/operand"
 	. "github.com/mmcloughlin/avo/reg"
+
+	// Ensure "go mod tidy" doesn't remove the golang.org/x/crypto module
+	// dependency, which is necessary to access the field.Element type.
+	_ "golang.org/x/crypto/curve25519"
 )
 
 //go:generate go run . -out ../fe_amd64.s -stubs ../fe_amd64.go -pkg field
 
 func main() {
 	Package("golang.org/x/crypto/curve25519/internal/field")
-	Comment("//go:build amd64 && gc && !purego")
 	ConstraintExpr("amd64,gc,!purego")
 	feMul()
 	feSquare()
diff --git a/curve25519/internal/field/_asm/go.mod b/curve25519/internal/field/_asm/go.mod
index 1127ade..fbc78be 100644
--- a/curve25519/internal/field/_asm/go.mod
+++ b/curve25519/internal/field/_asm/go.mod
@@ -2,4 +2,9 @@ module asm
 
 go 1.16
 
-require github.com/mmcloughlin/avo v0.2.0
+require (
+	github.com/mmcloughlin/avo v0.2.0
+	golang.org/x/crypto v0.0.0
+)
+
+replace golang.org/x/crypto v0.0.0 => ../../../..
diff --git a/curve25519/internal/field/_asm/go.sum b/curve25519/internal/field/_asm/go.sum
index dae4777..e2361f6 100644
--- a/curve25519/internal/field/_asm/go.sum
+++ b/curve25519/internal/field/_asm/go.sum
@@ -10,14 +10,17 @@ golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20201021035429-f5854403a974/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
+golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200930185726-fdedc70b468f/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210119212857-b64e53b001e4/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210403161142-5e06dd20ab57 h1:F5Gozwx4I1xtr/sr/8CFbb57iKi3297KFs0QDbGN60A=
 golang.org/x/sys v0.0.0-20210403161142-5e06dd20ab57/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=