diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index 93027c4..71c7b15 100644
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -483,15 +483,15 @@
 
 	if fi, err := os.Stat(filepath.Join(modRoot, "vendor")); err == nil && fi.IsDir() {
 		modGo := "unspecified"
-		if index.goVersion != "" {
-			if semver.Compare("v"+index.goVersion, "v1.14") >= 0 {
+		if index.goVersionV != "" {
+			if semver.Compare(index.goVersionV, "v1.14") >= 0 {
 				// The Go version is at least 1.14, and a vendor directory exists.
 				// Set -mod=vendor by default.
 				cfg.BuildMod = "vendor"
 				cfg.BuildModReason = "Go version in go.mod is at least 1.14 and vendor directory exists."
 				return
 			} else {
-				modGo = index.goVersion
+				modGo = index.goVersionV[1:]
 			}
 		}
 
diff --git a/src/cmd/go/internal/modload/modfile.go b/src/cmd/go/internal/modload/modfile.go
index 9f4ec5a..9a166ca 100644
--- a/src/cmd/go/internal/modload/modfile.go
+++ b/src/cmd/go/internal/modload/modfile.go
@@ -20,7 +20,7 @@
 	data         []byte
 	dataNeedsFix bool // true if fixVersion applied a change while parsing data
 	module       module.Version
-	goVersion    string
+	goVersionV   string // GoVersion with "v" prefix
 	require      map[module.Version]requireMeta
 	replace      map[module.Version]module.Version
 	exclude      map[module.Version]bool
@@ -66,9 +66,11 @@
 		i.module = modFile.Module.Mod
 	}
 
-	i.goVersion = ""
+	i.goVersionV = ""
 	if modFile.Go != nil {
-		i.goVersion = modFile.Go.Version
+		// We're going to use the semver package to compare Go versions, so go ahead
+		// and add the "v" prefix it expects once instead of every time.
+		i.goVersionV = "v" + modFile.Go.Version
 	}
 
 	i.require = make(map[module.Version]requireMeta, len(modFile.Require))
@@ -114,11 +116,11 @@
 	}
 
 	if modFile.Go == nil {
-		if i.goVersion != "" {
+		if i.goVersionV != "" {
 			return true
 		}
-	} else if modFile.Go.Version != i.goVersion {
-		if i.goVersion == "" && cfg.BuildMod == "readonly" {
+	} else if "v"+modFile.Go.Version != i.goVersionV {
+		if i.goVersionV == "" && cfg.BuildMod == "readonly" {
 			// go.mod files did not always require a 'go' version, so do not error out
 			// if one is missing — we may be inside an older module in the module
 			// cache, and should bias toward providing useful behavior.
diff --git a/src/cmd/go/internal/modload/vendor.go b/src/cmd/go/internal/modload/vendor.go
index 71f68ef..9f34b82 100644
--- a/src/cmd/go/internal/modload/vendor.go
+++ b/src/cmd/go/internal/modload/vendor.go
@@ -133,7 +133,7 @@
 	readVendorList()
 
 	pre114 := false
-	if modFile.Go == nil || semver.Compare("v"+modFile.Go.Version, "v1.14") < 0 {
+	if semver.Compare(index.goVersionV, "v1.14") < 0 {
 		// Go versions before 1.14 did not include enough information in
 		// vendor/modules.txt to check for consistency.
 		// If we know that we're on an earlier version, relax the consistency check.
@@ -150,6 +150,8 @@
 		}
 	}
 
+	// Iterate over the Require directives in their original (not indexed) order
+	// so that the errors match the original file.
 	for _, r := range modFile.Require {
 		if !vendorMeta[r.Mod].Explicit {
 			if pre114 {