diff --git a/src/text/scanner/scanner.go b/src/text/scanner/scanner.go
index 893a4edbaf..62b3231e5e 100644
--- a/src/text/scanner/scanner.go
+++ b/src/text/scanner/scanner.go
@@ -322,6 +322,7 @@ func (s *Scanner) Peek() rune {
 }
 
 func (s *Scanner) error(msg string) {
+	s.tokEnd = s.srcPos - s.lastCharLen // make sure token text is terminated
 	s.ErrorCount++
 	if s.Error != nil {
 		s.Error(s, msg)
@@ -664,17 +665,18 @@ func (s *Scanner) Pos() (pos Position) {
 }
 
 // TokenText returns the string corresponding to the most recently scanned token.
-// Valid after calling Scan().
+// Valid after calling Scan and in calls of Scanner.Error.
 func (s *Scanner) TokenText() string {
 	if s.tokPos < 0 {
 		// no token text
 		return ""
 	}
 
-	if s.tokEnd < 0 {
+	if s.tokEnd < s.tokPos {
 		// if EOF was reached, s.tokEnd is set to -1 (s.srcPos == 0)
 		s.tokEnd = s.tokPos
 	}
+	// s.tokEnd >= s.tokPos
 
 	if s.tokBuf.Len() == 0 {
 		// common case: the entire token text is still in srcBuf
diff --git a/src/text/scanner/scanner_test.go b/src/text/scanner/scanner_test.go
index e26e816f51..e7539a058b 100644
--- a/src/text/scanner/scanner_test.go
+++ b/src/text/scanner/scanner_test.go
@@ -293,6 +293,12 @@ func TestScan(t *testing.T) {
 func TestIllegalExponent(t *testing.T) {
 	const src = "1.5e 1.5E 1e+ 1e- 1.5z"
 	s := new(Scanner).Init(strings.NewReader(src))
+	s.Error = func(s *Scanner, msg string) {
+		const want = "illegal exponent"
+		if msg != want {
+			t.Errorf("%s: got error %q; want %q", s.TokenText(), msg, want)
+		}
+	}
 	checkTokErr(t, s, 1, Float, "1.5e")
 	checkTokErr(t, s, 1, Float, "1.5E")
 	checkTokErr(t, s, 1, Float, "1e+")
@@ -692,3 +698,16 @@ func TestScanEOFHandling(t *testing.T) {
 		t.Errorf("scanner called Read %d times, not once", r)
 	}
 }
+
+func TestIssue29723(t *testing.T) {
+	s := new(Scanner).Init(strings.NewReader(`x "`))
+	s.Error = func(s *Scanner, _ string) {
+		got := s.TokenText() // this call shouldn't panic
+		const want = `"`
+		if got != want {
+			t.Errorf("got %q; want %q", got, want)
+		}
+	}
+	for r := s.Scan(); r != EOF; r = s.Scan() {
+	}
+}