diff --git a/flags_test.go b/flags_test.go
index b8969a9..db1564e 100644
--- a/flags_test.go
+++ b/flags_test.go
@@ -29,6 +29,17 @@ func TestIgnoredLoggerFlag(t *testing.T) {
 	assert.ErrorContains(t, err, "-ignoredloggers: unknown logger: \"unknownlogger\"")
 }
 
+func TestNoRuleFile(t *testing.T) {
+	f := ruleFileFlag{}
+
+	fs := flag.NewFlagSet("test", flag.ContinueOnError)
+	fs.SetOutput(io.Discard)
+	fs.Var(&f, "rulefile", "")
+
+	err := fs.Parse([]string{"-rulefile=testdata/xxx-not-exists-xxx.txt"})
+	assert.ErrorContains(t, err, "open testdata/xxx-not-exists-xxx.txt: no such file or directory")
+}
+
 func TestWrongRuleFile(t *testing.T) {
 	f := ruleFileFlag{}
 
@@ -36,6 +47,6 @@ func TestWrongRuleFile(t *testing.T) {
 	fs.SetOutput(io.Discard)
 	fs.Var(&f, "rulefile", "")
 
-	err := fs.Parse([]string{"-rulefile=testdata/xxx-not-exists-xxx.yaml"})
-	assert.ErrorContains(t, err, "open testdata/xxx-not-exists-xxx.yaml: no such file or directory")
+	err := fs.Parse([]string{"-rulefile=testdata/wrong-rules.txt"})
+	assert.ErrorContains(t, err, "error parse rule at line 2: invalid rule format")
 }
diff --git a/rules/rules.go b/rules/rules.go
index 1b54e6b..df425f3 100644
--- a/rules/rules.go
+++ b/rules/rules.go
@@ -12,7 +12,7 @@ import (
 	"github.com/timonwong/loggercheck/internal/bytebufferpool"
 )
 
-var ErrInvalidRule = errors.New("invalid rule")
+var ErrInvalidRule = errors.New("invalid rule format")
 
 type RulesetList []Ruleset
 
diff --git a/checker.go b/staticrules.go
similarity index 100%
rename from checker.go
rename to staticrules.go
diff --git a/testdata/wrong-rules.txt b/testdata/wrong-rules.txt
new file mode 100644
index 0000000..c044ee5
--- /dev/null
+++ b/testdata/wrong-rules.txt
@@ -0,0 +1,2 @@
+# Wrong rule file
+(*a/wrong.Method.Rule