diff --git a/src/cmd/go/internal/load/pkg.go b/src/cmd/go/internal/load/pkg.go
index a5be48a..dfe7849 100644
--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -25,6 +25,7 @@
 	"sort"
 	"strconv"
 	"strings"
+	"time"
 	"unicode"
 	"unicode/utf8"
 
@@ -2364,10 +2365,14 @@
 			setVCSError(err)
 			return
 		}
-		info.Settings = append(info.Settings, []debug.BuildSetting{
-			{Key: vcsCmd.Cmd + "revision", Value: st.Revision},
-			{Key: vcsCmd.Cmd + "uncommitted", Value: strconv.FormatBool(st.Uncommitted)},
-		}...)
+		if st.Revision != "" {
+			appendSetting(vcsCmd.Cmd+"revision", st.Revision)
+		}
+		if !st.CommitTime.IsZero() {
+			stamp := st.CommitTime.UTC().Format(time.RFC3339Nano)
+			appendSetting(vcsCmd.Cmd+"committime", stamp)
+		}
+		appendSetting(vcsCmd.Cmd+"uncommitted", strconv.FormatBool(st.Uncommitted))
 	}
 
 	text, err := info.MarshalText()
diff --git a/src/cmd/go/internal/vcs/vcs.go b/src/cmd/go/internal/vcs/vcs.go
index d1272b6..941bd57 100644
--- a/src/cmd/go/internal/vcs/vcs.go
+++ b/src/cmd/go/internal/vcs/vcs.go
@@ -18,8 +18,10 @@
 	"os"
 	"path/filepath"
 	"regexp"
+	"strconv"
 	"strings"
 	"sync"
+	"time"
 
 	"cmd/go/internal/base"
 	"cmd/go/internal/cfg"
@@ -54,8 +56,9 @@
 
 // Status is the current state of a local repository.
 type Status struct {
-	Revision    string
-	Uncommitted bool
+	Revision    string    // Optional.
+	CommitTime  time.Time // Optional.
+	Uncommitted bool      // Required.
 }
 
 var defaultSecureScheme = map[string]bool{
@@ -159,24 +162,52 @@
 }
 
 func hgStatus(vcsHg *Cmd, rootDir string) (Status, error) {
-	out, err := vcsHg.runOutputVerboseOnly(rootDir, "identify -i")
+	// Output changeset ID and seconds since epoch.
+	out, err := vcsHg.runOutputVerboseOnly(rootDir, `log -l1 -T {node}:{date(date,"%s")}`)
 	if err != nil {
 		return Status{}, err
 	}
-	rev := strings.TrimSpace(string(out))
-	uncommitted := strings.HasSuffix(rev, "+")
-	if uncommitted {
-		// "+" means a tracked file is edited.
-		rev = rev[:len(rev)-len("+")]
-	} else {
-		// Also look for untracked files.
-		out, err = vcsHg.runOutputVerboseOnly(rootDir, "status -u")
+
+	// Successful execution without output indicates an empty repo (no commits).
+	var rev string
+	var commitTime time.Time
+	if len(out) > 0 {
+		rev, commitTime, err = parseRevTime(out)
 		if err != nil {
 			return Status{}, err
 		}
-		uncommitted = len(out) > 0
 	}
-	return Status{Revision: rev, Uncommitted: uncommitted}, nil
+
+	// Also look for untracked files.
+	out, err = vcsHg.runOutputVerboseOnly(rootDir, "status")
+	if err != nil {
+		return Status{}, err
+	}
+	uncommitted := len(out) > 0
+
+	return Status{
+		Revision:    rev,
+		CommitTime:  commitTime,
+		Uncommitted: uncommitted,
+	}, nil
+}
+
+// parseRevTime parses commit details in "revision:seconds" format.
+func parseRevTime(out []byte) (string, time.Time, error) {
+	buf := string(bytes.TrimSpace(out))
+
+	i := strings.IndexByte(buf, ':')
+	if i < 1 {
+		return "", time.Time{}, errors.New("unrecognized VCS tool output")
+	}
+	rev := buf[:i]
+
+	secs, err := strconv.ParseInt(string(buf[i+1:]), 10, 64)
+	if err != nil {
+		return "", time.Time{}, fmt.Errorf("unrecognized VCS tool output: %v", err)
+	}
+
+	return rev, time.Unix(secs, 0), nil
 }
 
 // vcsGit describes how to use Git.
@@ -263,18 +294,33 @@
 	return "", errParse
 }
 
-func gitStatus(cmd *Cmd, repoDir string) (Status, error) {
-	out, err := cmd.runOutputVerboseOnly(repoDir, "rev-parse HEAD")
+func gitStatus(vcsGit *Cmd, rootDir string) (Status, error) {
+	out, err := vcsGit.runOutputVerboseOnly(rootDir, "status --porcelain")
 	if err != nil {
 		return Status{}, err
 	}
-	rev := string(bytes.TrimSpace(out))
-	out, err = cmd.runOutputVerboseOnly(repoDir, "status --porcelain")
-	if err != nil {
+	uncommitted := len(out) > 0
+
+	// "git status" works for empty repositories, but "git show" does not.
+	// Assume there are no commits in the repo when "git show" fails with
+	// uncommitted files and skip tagging revision / committime.
+	var rev string
+	var commitTime time.Time
+	out, err = vcsGit.runOutputVerboseOnly(rootDir, "show -s --format=%H:%ct")
+	if err != nil && !uncommitted {
 		return Status{}, err
+	} else if err == nil {
+		rev, commitTime, err = parseRevTime(out)
+		if err != nil {
+			return Status{}, err
+		}
 	}
-	uncommitted := len(out) != 0
-	return Status{Revision: rev, Uncommitted: uncommitted}, nil
+
+	return Status{
+		Revision:    rev,
+		CommitTime:  commitTime,
+		Uncommitted: uncommitted,
+	}, nil
 }
 
 // vcsBzr describes how to use Bazaar.
diff --git a/src/cmd/go/testdata/script/version_buildvcs_git.txt b/src/cmd/go/testdata/script/version_buildvcs_git.txt
index 78ce2e8..3d56c6d 100644
--- a/src/cmd/go/testdata/script/version_buildvcs_git.txt
+++ b/src/cmd/go/testdata/script/version_buildvcs_git.txt
@@ -28,16 +28,25 @@
 env PATH=$oldpath
 rm .git
 
-# If there is a repository in a parent directory, there should be VCS info.
+# If there is an empty repository in a parent directory, only "uncommitted" is tagged.
 exec git init
 exec git config user.email gopher@golang.org
 exec git config user.name 'J.R. Gopher'
-exec git add -A
-exec git commit -m 'initial commit'
 cd a
 go install
 go version -m $GOBIN/a$GOEXE
+! stdout gitrevision
+! stdout gitcommittime
+stdout '^\tbuild\tgituncommitted\ttrue$'
+rm $GOBIN/a$GOEXE
+
+# Revision and commit time are tagged for repositories with commits.
+exec git add -A
+exec git commit -m 'initial commit'
+go install
+go version -m $GOBIN/a$GOEXE
 stdout '^\tbuild\tgitrevision\t'
+stdout '^\tbuild\tgitcommittime\t'
 stdout '^\tbuild\tgituncommitted\tfalse$'
 rm $GOBIN/a$GOEXE
 
diff --git a/src/cmd/go/testdata/script/version_buildvcs_hg.txt b/src/cmd/go/testdata/script/version_buildvcs_hg.txt
index 9dcb8dd..df49387 100644
--- a/src/cmd/go/testdata/script/version_buildvcs_hg.txt
+++ b/src/cmd/go/testdata/script/version_buildvcs_hg.txt
@@ -29,14 +29,24 @@
 env PATH=$oldpath
 rm .hg
 
-# If there is a repository in a parent directory, there should be VCS info.
+# If there is an empty repository in a parent directory, only "uncommitted" is tagged.
 exec hg init
+cd a
+go install
+go version -m $GOBIN/a$GOEXE
+! stdout hgrevision
+! stdout hgcommittime
+stdout '^\tbuild\thguncommitted\ttrue$'
+cd ..
+
+# Revision and commit time are tagged for repositories with commits.
 exec hg add a README
 exec hg commit -m 'initial commit'
 cd a
 go install
 go version -m $GOBIN/a$GOEXE
 stdout '^\tbuild\thgrevision\t'
+stdout '^\tbuild\thgcommittime\t'
 stdout '^\tbuild\thguncommitted\tfalse$'
 rm $GOBIN/a$GOEXE