diff --git a/.github/workflows/go.yml b/.github/workflows/go.yml
index 57662e33..8b643af9 100644
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -10,7 +10,7 @@ jobs:
   Test:
     strategy:
       matrix:
-        go-version: [1.18.x, 1.21.x]
+        go-version: [1.19.x, 1.21.x]
         os: [ubuntu-latest, windows-latest, macos-latest]
     runs-on: ${{ matrix.os }}
     steps:
diff --git a/go.mod b/go.mod
index 461f621b..daf4b616 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/goplus/gogen
 
-go 1.18
+go 1.19
 
 require golang.org/x/tools v0.19.0
 
diff --git a/internal/go/printer/printer.go b/internal/go/printer/printer.go
index a4897835..a2b9582f 100644
--- a/internal/go/printer/printer.go
+++ b/internal/go/printer/printer.go
@@ -609,7 +609,7 @@ func stripCommonPrefix(lines []string) {
 	last := lines[len(lines)-1]
 	closing := "*/"
 	i := strings.Index(last, closing) // i >= 0 (closing is always present)
-	if isBlank(last[0:i]) {
+	if i >= 0 && isBlank(last[0:i]) {
 		// last line only contains closing */
 		if lineOfStars {
 			closing = " */" // add blank to align final star