diff --git a/.gitignore b/.gitignore
index 8365624..4b7b1f9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -21,3 +21,6 @@ _testmain.go
 
 *.exe
 *.test
+
+# 
+*.out
diff --git a/pop3proto.go b/pop3proto.go
index e6c9b1b..ac972c0 100644
--- a/pop3proto.go
+++ b/pop3proto.go
@@ -110,18 +110,17 @@ func (r *Reader) ReadResponse() (string, error) {
 }
 
 func (r *Reader) parseResponse(line string) (string, error) {
-	var index int
+	s := strings.ToUpper(line)
 
-	if index = strings.Index(line, " "); index < 0 {
-		return "", ResponseError(fmt.Sprintf("invalid response format: %s", line))
-	}
-
-	switch strings.ToUpper(line[:index]) {
-	case "+OK":
-		return line[index+1:], nil
-	case "-ERR":
-		return "", ResponseError(line[index+1:])
-	default:
+	if s == "+OK" {
+		return "", nil
+	} else if strings.HasPrefix(s, "+OK ") {
+		return line[4:], nil
+	} else if s == "-ERR" {
+		return "", ResponseError("")
+	} else if strings.HasPrefix(s, "-ERR ") {
+		return "", ResponseError(line[5:])
+	} else {
 		return "", ResponseError(fmt.Sprintf("unknown response: %s", line))
 	}
 }
diff --git a/pop3proto_test.go b/pop3proto_test.go
index 835c02c..215ff79 100644
--- a/pop3proto_test.go
+++ b/pop3proto_test.go
@@ -59,15 +59,51 @@ func TestReadResponse(t *testing.T) {
 		t.Fatalf("%v, %v", s, err)
 	}
 
+	r = reader("+OK\n")
+	s, err = r.ReadResponse()
+	if s != "" || err != nil {
+		t.Fatalf("%v, %v", s, err)
+	}
+
+	r = reader("+OK \n")
+	s, err = r.ReadResponse()
+	if s != "" || err != nil {
+		t.Fatalf("%v, %v", s, err)
+	}
+
+	r = reader("+OKAY\n")
+	s, err = r.ReadResponse()
+	if s != "" || err == nil || err.Error() != "unknown response: +OKAY" {
+		t.Fatalf("%v, %v", s, err)
+	}
+
 	r = reader("-ERR message\n")
 	s, err = r.ReadResponse()
 	if s != "" || err == nil || err.Error() != "message" {
 		t.Fatalf("%v, %v", s, err)
 	}
 
+	r = reader("-ERR\n")
+	s, err = r.ReadResponse()
+	if s != "" || err == nil || err.Error() != "" {
+		t.Fatalf("%v, %v", s, err)
+	}
+
+	r = reader("-ERR \n")
+	s, err = r.ReadResponse()
+	if s != "" || err == nil || err.Error() != "" {
+		t.Fatalf("%v, %v", s, err)
+	}
+
+	r = reader("-ERROR\n")
+	s, err = r.ReadResponse()
+	if s != "" || err == nil || err.Error() != "unknown response: -ERROR" {
+		t.Fatalf("%v, %v", s, err)
+	}
+
 	r = reader("message\n")
 	s, err = r.ReadResponse()
-	if s != "" || err == nil || err.Error() != "invalid response format: message" {
+	if s != "" || err == nil || err.Error() != "unknown response: message" {
 		t.Fatalf("%v, %v", s, err)
 	}
 
@@ -76,6 +112,18 @@ func TestReadResponse(t *testing.T) {
 	if s != "" || err == nil || err.Error() != "unknown response: * message" {
 		t.Fatalf("%v, %v", s, err)
 	}
+
+	r = reader(" message\n")
+	s, err = r.ReadResponse()
+	if s != "" || err == nil || err.Error() != "unknown response:  message" {
+		t.Fatalf("%v, %v", s, err)
+	}
+
+	r = reader("\n")
+	s, err = r.ReadResponse()
+	if s != "" || err == nil || err.Error() != "unknown response: " {
+		t.Fatalf("%v, %v", s, err)
+	}
 }
 
 func TestWriteLine(t *testing.T) {