diff --git a/internal/fs.go b/internal/fs.go
index b531baf..232f096 100644
--- a/internal/fs.go
+++ b/internal/fs.go
@@ -12,9 +12,12 @@ func ReplaceOnce(path string, re *regexp.Regexp, replace string) error {
 		return err
 	}
 	orig := string(data)
+	if !re.MatchString(orig) {
+		return fmt.Errorf("pattern not found in %s", path)
+	}
 	out := re.ReplaceAllString(orig, replace)
 	if out == orig {
-		return fmt.Errorf("pattern not found in %s", path)
+		return nil
 	}
 	return os.WriteFile(path, []byte(out), 0644)
 }
@@ -25,9 +28,12 @@ func ReplaceOnceFunc(path string, re *regexp.Regexp, fn func(string) string) err
 		return err
 	}
 	orig := string(data)
+	if !re.MatchString(orig) {
+		return fmt.Errorf("pattern not found in %s", path)
+	}
 	out := re.ReplaceAllStringFunc(orig, fn)
 	if out == orig {
-		return fmt.Errorf("pattern not found in %s", path)
+		return nil
 	}
 	return os.WriteFile(path, []byte(out), 0644)
 }