diff --git a/src/go/scanner/scanner.go b/src/go/scanner/scanner.go
index 29cbf39721..f08e28cdd6 100644
--- a/src/go/scanner/scanner.go
+++ b/src/go/scanner/scanner.go
@@ -373,7 +373,7 @@ func (s *Scanner) scanIdentifier() string {
 			continue
 		}
 		s.rdOffset += rdOffset
-		if b < utf8.RuneSelf {
+		if 0 < b && b < utf8.RuneSelf {
 			// Optimization: we've encountered an ASCII character that's not a letter
 			// or number. Avoid the call into s.next() and corresponding set up.
 			//
diff --git a/src/go/scanner/scanner_test.go b/src/go/scanner/scanner_test.go
index ac8d257716..db123c32e0 100644
--- a/src/go/scanner/scanner_test.go
+++ b/src/go/scanner/scanner_test.go
@@ -812,6 +812,8 @@ var errors = []struct {
 	{"//\ufeff", token.COMMENT, 2, "//\ufeff", "illegal byte order mark"},                                // only first BOM is ignored
 	{"'\ufeff" + `'`, token.CHAR, 1, "'\ufeff" + `'`, "illegal byte order mark"},                         // only first BOM is ignored
 	{`"` + "abc\ufeffdef" + `"`, token.STRING, 4, `"` + "abc\ufeffdef" + `"`, "illegal byte order mark"}, // only first BOM is ignored
+	{"abc\x00def", token.IDENT, 3, "abc", "illegal character NUL"},
+	{"abc\x00", token.IDENT, 3, "abc", "illegal character NUL"},
 }
 
 func TestScanErrors(t *testing.T) {