diff --git a/examples/keyboard/keyboard/gen.go b/examples/keyboard/keyboard/gen.go
index c0bdf9c38..3ab350dce 100644
--- a/examples/keyboard/keyboard/gen.go
+++ b/examples/keyboard/keyboard/gen.go
@@ -263,7 +263,7 @@ func outputKeyboardImage() (map[ebiten.Key]image.Rectangle, error) {
 
 const keyRectTmpl = `{{.License}}
 
-// Code generated by gen.go using 'go generate'. DO NOT EDIT
+// Code generated by gen.go using 'go generate'. DO NOT EDIT.
 
 package keyboard
 
diff --git a/examples/keyboard/keyboard/keyrects.go b/examples/keyboard/keyboard/keyrects.go
index 1d1a3f3f4..48a52b13c 100644
--- a/examples/keyboard/keyboard/keyrects.go
+++ b/examples/keyboard/keyboard/keyrects.go
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Code generated by gen.go using 'go generate'. DO NOT EDIT
+// Code generated by gen.go using 'go generate'. DO NOT EDIT.
 
 package keyboard
 
diff --git a/internal/png/gen.go b/internal/png/gen.go
index 89650aa47..2c547e580 100644
--- a/internal/png/gen.go
+++ b/internal/png/gen.go
@@ -95,7 +95,7 @@ func run() error {
 			return true
 		}, nil)
 
-		fmt.Fprintln(out, "// Code generated by gen.go. DO NOT EDIT")
+		fmt.Fprintln(out, "// Code generated by gen.go. DO NOT EDIT.")
 		fmt.Fprintln(out)
 		format.Node(out, fset, tree)
 	}
diff --git a/internal/png/stdlibpaeth.go b/internal/png/stdlibpaeth.go
index 19a38dbd4..3f8fc097f 100644
--- a/internal/png/stdlibpaeth.go
+++ b/internal/png/stdlibpaeth.go
@@ -1,4 +1,4 @@
-// Code generated by gen.go. DO NOT EDIT
+// Code generated by gen.go. DO NOT EDIT.
 
 // Copyright 2012 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
diff --git a/internal/png/stdlibreader.go b/internal/png/stdlibreader.go
index 6a834ff09..d7d589746 100644
--- a/internal/png/stdlibreader.go
+++ b/internal/png/stdlibreader.go
@@ -1,4 +1,4 @@
-// Code generated by gen.go. DO NOT EDIT
+// Code generated by gen.go. DO NOT EDIT.
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
diff --git a/internal/png/stdlibwriter.go b/internal/png/stdlibwriter.go
index feb792ec6..5e9448b2d 100644
--- a/internal/png/stdlibwriter.go
+++ b/internal/png/stdlibwriter.go
@@ -1,4 +1,4 @@
-// Code generated by gen.go. DO NOT EDIT
+// Code generated by gen.go. DO NOT EDIT.
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style