diff --git a/signal/signal.go b/signal/signal.go
index c9cd046c..3fbf1aac 100644
--- a/signal/signal.go
+++ b/signal/signal.go
@@ -39,13 +39,13 @@ func ParseSignal(rawSignal string) (syscall.Signal, error) {
 	s, err := strconv.Atoi(rawSignal)
 	if err == nil {
 		if s == 0 {
-			return -1, fmt.Errorf("Invalid signal: %s", rawSignal)
+			return -1, fmt.Errorf("invalid signal: %s", rawSignal)
 		}
 		return syscall.Signal(s), nil
 	}
 	signal, ok := SignalMap[strings.TrimPrefix(strings.ToUpper(rawSignal), "SIG")]
 	if !ok {
-		return -1, fmt.Errorf("Invalid signal: %s", rawSignal)
+		return -1, fmt.Errorf("invalid signal: %s", rawSignal)
 	}
 	return signal, nil
 }
diff --git a/signal/signal_test.go b/signal/signal_test.go
index b51c03ff..b8616947 100644
--- a/signal/signal_test.go
+++ b/signal/signal_test.go
@@ -7,13 +7,13 @@ import (
 
 func TestParseSignal(t *testing.T) {
 	_, err := ParseSignal("0")
-	expectedErr := "Invalid signal: 0"
+	expectedErr := "invalid signal: 0"
 	if err == nil || err.Error() != expectedErr {
 		t.Errorf("expected  %q, but got %v", expectedErr, err)
 	}
 
 	_, err = ParseSignal("SIG")
-	expectedErr = "Invalid signal: SIG"
+	expectedErr = "invalid signal: SIG"
 	if err == nil || err.Error() != expectedErr {
 		t.Errorf("expected  %q, but got %v", expectedErr, err)
 	}