diff --git a/src/cmd/go.mod b/src/cmd/go.mod
index c3617eea0b..88f5f2883a 100644
--- a/src/cmd/go.mod
+++ b/src/cmd/go.mod
@@ -7,7 +7,7 @@ require (
 	github.com/ianlancetaylor/demangle v0.0.0-20200824232613-28f6c0f3b639 // indirect
 	golang.org/x/arch v0.0.0-20210502124803-cbf565b21d1e
 	golang.org/x/crypto v0.0.0-20210503195802-e9a32991a82e // indirect
-	golang.org/x/mod v0.4.3-0.20210504181020-67f1c1edc27a
+	golang.org/x/mod v0.4.3-0.20210512182355-6088ed88cecd
 	golang.org/x/sys v0.0.0-20210511113859-b0526f3d8744 // indirect
 	golang.org/x/term v0.0.0-20210503060354-a79de5458b56
 	golang.org/x/tools v0.1.1-0.20210505014545-7cab0ef2e9a5
diff --git a/src/cmd/go.sum b/src/cmd/go.sum
index f42aac70d6..73750802bc 100644
--- a/src/cmd/go.sum
+++ b/src/cmd/go.sum
@@ -9,8 +9,8 @@ golang.org/x/arch v0.0.0-20210502124803-cbf565b21d1e h1:pv3V0NlNSh5Q6AX/StwGLBjc
 golang.org/x/arch v0.0.0-20210502124803-cbf565b21d1e/go.mod h1:5om86z9Hs0C8fWVUuoMHwpExlXzs5Tkyp9hOrfG7pp8=
 golang.org/x/crypto v0.0.0-20210503195802-e9a32991a82e h1:8foAy0aoO5GkqCvAEJ4VC4P3zksTg4X4aJCDpZzmgQI=
 golang.org/x/crypto v0.0.0-20210503195802-e9a32991a82e/go.mod h1:P+XmwS30IXTQdn5tA2iutPOUgjI07+tq3H3K9MVA1s8=
-golang.org/x/mod v0.4.3-0.20210504181020-67f1c1edc27a h1:wbpC/7Wbo5WFVox32n+KjhRRLmTLq8YW/wRlL2iVAhk=
-golang.org/x/mod v0.4.3-0.20210504181020-67f1c1edc27a/go.mod h1:5OXOZSfqPIIbmVBIIKWRFfZjPR0E5r58TLhUjH0a2Ro=
+golang.org/x/mod v0.4.3-0.20210512182355-6088ed88cecd h1:CuRnpyMrCCBulv0d/y0CswR4K0vGydgE3DZ2wYPIOo8=
+golang.org/x/mod v0.4.3-0.20210512182355-6088ed88cecd/go.mod h1:5OXOZSfqPIIbmVBIIKWRFfZjPR0E5r58TLhUjH0a2Ro=
 golang.org/x/sys v0.0.0-20191204072324-ce4227a45e2e/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210511113859-b0526f3d8744 h1:yhBbb4IRs2HS9PPlAg6DMC6mUOKexJBNsLf4Z+6En1Q=
 golang.org/x/sys v0.0.0-20210511113859-b0526f3d8744/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
diff --git a/src/cmd/go/testdata/script/badgo.txt b/src/cmd/go/testdata/script/badgo.txt
new file mode 100644
index 0000000000..cf4e2584d6
--- /dev/null
+++ b/src/cmd/go/testdata/script/badgo.txt
@@ -0,0 +1,50 @@
+go get example.net/badgo@v1.0.0
+go get example.net/badgo@v1.1.0
+go get example.net/badgo@v1.2.0
+go get example.net/badgo@v1.3.0
+go get example.net/badgo@v1.4.0
+go get example.net/badgo@v1.5.0
+! go get example.net/badgo@v1.6.0
+stderr 'invalid go version .X.Y.: must match format 1.23'
+
+-- go.mod --
+module m
+
+replace (
+	example.net/badgo v1.0.0 => ./v1.0.0
+	example.net/badgo v1.1.0 => ./v1.1.0
+	example.net/badgo v1.2.0 => ./v1.2.0
+	example.net/badgo v1.3.0 => ./v1.3.0
+	example.net/badgo v1.4.0 => ./v1.4.0
+	example.net/badgo v1.5.0 => ./v1.5.0
+	example.net/badgo v1.6.0 => ./v1.6.0
+)
+
+-- v1.0.0/go.mod --
+module example.net/badgo
+go 1.17.0
+
+-- v1.1.0/go.mod --
+module example.net/badgo
+go 1.17rc2
+
+-- v1.2.0/go.mod --
+module example.net/badgo
+go 1.17.1
+
+-- v1.3.0/go.mod --
+module example.net/badgo
+go v1.17.0
+
+-- v1.4.0/go.mod --
+module example.net/badgo
+go v1.17.0-rc.2
+
+-- v1.5.0/go.mod --
+module example.net/badgo
+go v1.17.1
+
+-- v1.6.0/go.mod --
+module example.net/badgo
+go X.Y
+
diff --git a/src/cmd/vendor/golang.org/x/mod/modfile/rule.go b/src/cmd/vendor/golang.org/x/mod/modfile/rule.go
index d8242de280..7299e15500 100644
--- a/src/cmd/vendor/golang.org/x/mod/modfile/rule.go
+++ b/src/cmd/vendor/golang.org/x/mod/modfile/rule.go
@@ -217,6 +217,7 @@ func parseToFile(file string, data []byte, fix VersionFixer, strict bool) (parse
 }
 
 var GoVersionRE = lazyregexp.New(`^([1-9][0-9]*)\.(0|[1-9][0-9]*)$`)
+var laxGoVersionRE = lazyregexp.New(`^v?(([1-9][0-9]*)\.(0|[1-9][0-9]*))([^0-9].*)$`)
 
 func (f *File) add(errs *ErrorList, block *LineBlock, line *Line, verb string, args []string, fix VersionFixer, strict bool) {
 	// If strict is false, this module is a dependency.
@@ -267,8 +268,17 @@ func (f *File) add(errs *ErrorList, block *LineBlock, line *Line, verb string, a
 			errorf("go directive expects exactly one argument")
 			return
 		} else if !GoVersionRE.MatchString(args[0]) {
-			errorf("invalid go version '%s': must match format 1.23", args[0])
-			return
+			fixed := false
+			if !strict {
+				if m := laxGoVersionRE.FindStringSubmatch(args[0]); m != nil {
+					args[0] = m[1]
+					fixed = true
+				}
+			}
+			if !fixed {
+				errorf("invalid go version '%s': must match format 1.23", args[0])
+				return
+			}
 		}
 
 		f.Go = &Go{Syntax: line}
diff --git a/src/cmd/vendor/modules.txt b/src/cmd/vendor/modules.txt
index 10591f8041..016ec011a9 100644
--- a/src/cmd/vendor/modules.txt
+++ b/src/cmd/vendor/modules.txt
@@ -28,7 +28,7 @@ golang.org/x/arch/x86/x86asm
 ## explicit; go 1.17
 golang.org/x/crypto/ed25519
 golang.org/x/crypto/ed25519/internal/edwards25519
-# golang.org/x/mod v0.4.3-0.20210504181020-67f1c1edc27a
+# golang.org/x/mod v0.4.3-0.20210512182355-6088ed88cecd
 ## explicit; go 1.17
 golang.org/x/mod/internal/lazyregexp
 golang.org/x/mod/modfile