diff --git a/src/cmd/go/internal/module/module.go b/src/cmd/go/internal/module/module.go
index 629aca1..11a45e0 100644
--- a/src/cmd/go/internal/module/module.go
+++ b/src/cmd/go/internal/module/module.go
@@ -12,6 +12,9 @@
 // There are many subtle considerations, including Unicode ambiguity,
 // security, network, and file system representations.
 //
+// This file also defines the set of valid module path and version combinations,
+// another topic with many subtle considerations.
+//
 // Changes to the semantics in this file require approval from rsc.
 
 import (
@@ -50,31 +53,17 @@
 	if !semver.IsValid(version) {
 		return fmt.Errorf("malformed semantic version %v", version)
 	}
-	vm := semver.Major(version)
-	_, pathVersion, _ := SplitPathVersion(path)
-
-	if strings.HasPrefix(pathVersion, ".") {
-		// Special-case gopkg.in path requirements.
-		pathVersion = pathVersion[1:] // cut .
-		if vm == pathVersion {
-			return nil
+	_, pathMajor, _ := SplitPathVersion(path)
+	if !MatchPathMajor(version, pathMajor) {
+		if pathMajor == "" {
+			pathMajor = "v0 or v1"
 		}
-	} else {
-		// Standard path requirements.
-		if pathVersion != "" {
-			pathVersion = pathVersion[1:] // cut /
+		if pathMajor[0] == '.' { // .v1
+			pathMajor = pathMajor[1:]
 		}
-		if vm == "v0" || vm == "v1" {
-			vm = ""
-		}
-		if vm == pathVersion {
-			return nil
-		}
-		if pathVersion == "" {
-			pathVersion = "v0 or v1"
-		}
+		return fmt.Errorf("mismatched module path %v and version %v (want %v)", path, version, pathMajor)
 	}
-	return fmt.Errorf("mismatched module path %v and version %v (want %v)", path, version, pathVersion)
+	return nil
 }
 
 // firstPathOK reports whether r can appear in the first element of a module path.
@@ -328,6 +317,11 @@
 // MatchPathMajor reports whether the semantic version v
 // matches the path major version pathMajor.
 func MatchPathMajor(v, pathMajor string) bool {
+	if strings.HasPrefix(v, "v0.0.0-") && pathMajor == ".v1" {
+		// Allow old bug in pseudo-versions that generated v0.0.0- pseudoversion for gopkg .v1.
+		// For example, gopkg.in/yaml.v2@v2.2.1's go.mod requires gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405.
+		return true
+	}
 	m := semver.Major(v)
 	if pathMajor == "" {
 		return m == "v0" || m == "v1"
diff --git a/src/cmd/go/internal/module/module_test.go b/src/cmd/go/internal/module/module_test.go
index 83e8d1a..686e289 100644
--- a/src/cmd/go/internal/module/module_test.go
+++ b/src/cmd/go/internal/module/module_test.go
@@ -37,6 +37,14 @@
 	{"gopkg.in/yaml.v1", "v2.1.5", false},
 	{"gopkg.in/yaml.v1", "v3.0.0", false},
 
+	// For gopkg.in, .v1 means v1 only (not v0).
+	// But early versions of vgo still generated v0 pseudo-versions for it.
+	// Even though now we'd generate those as v1 pseudo-versions,
+	// we accept the old pseudo-versions to avoid breaking existing go.mod files.
+	// For example gopkg.in/yaml.v2@v2.2.1's go.mod requires check.v1 at a v0 pseudo-version.
+	{"gopkg.in/check.v1", "v0.0.0", false},
+	{"gopkg.in/check.v1", "v0.0.0-20160102150405-abcdef123456", true},
+
 	{"gopkg.in/yaml.v2", "v1.0.0", false},
 	{"gopkg.in/yaml.v2", "v2.0.0", true},
 	{"gopkg.in/yaml.v2", "v2.1.5", true},
diff --git a/src/cmd/go/mod_test.go b/src/cmd/go/mod_test.go
index 3e8a010..0199559 100644
--- a/src/cmd/go/mod_test.go
+++ b/src/cmd/go/mod_test.go
@@ -834,14 +834,12 @@
 		"rsc.io/badfile3",
 		"rsc.io/badfile4",
 		"rsc.io/badfile5",
-		"rsc.io/badfile6",
 	)
 	tg.grepStderrNot(`unzip .*badfile1.*:`, "badfile1 should be OK")
 	tg.grepStderr(`rsc.io/badfile2.*malformed file path "☺.go": invalid char '☺'`, "want diagnosed invalid character")
-	tg.grepStderr(`rsc.io/badfile3.*malformed file path "x@y.go": invalid char '@'`, "want diagnosed invalid character")
+	tg.grepStderr(`rsc.io/badfile3.*malformed file path "x\?y.go": invalid char '\?'`, "want diagnosed invalid character")
 	tg.grepStderr(`rsc.io/badfile4.*case-insensitive file name collision: "x/Y.go" and "x/y.go"`, "want case collision")
 	tg.grepStderr(`rsc.io/badfile5.*case-insensitive file name collision: "x/y" and "x/Y"`, "want case collision")
-	tg.grepStderr(`rsc.io/badfile6.*malformed file path "x/.gitignore/y": leading dot in path element`, "want leading dot in path element")
 }
 
 func TestModBadDomain(t *testing.T) {
diff --git a/src/cmd/go/testdata/mod/rsc.io_badfile3_v1.0.0.txt b/src/cmd/go/testdata/mod/rsc.io_badfile3_v1.0.0.txt
index 91bd65f..a008448 100644
--- a/src/cmd/go/testdata/mod/rsc.io_badfile3_v1.0.0.txt
+++ b/src/cmd/go/testdata/mod/rsc.io_badfile3_v1.0.0.txt
@@ -7,6 +7,6 @@
 {"Version":"v1.0.0"}
 -- go.mod --
 module rsc.io/badfile3
--- x@y.go --
+-- x?y.go --
 package x