diff --git a/libraries/AP_GPS/AP_GPS_MTK19.cpp b/libraries/AP_GPS/AP_GPS_MTK19.cpp
index a5033197d1..7e873cce55 100644
--- a/libraries/AP_GPS/AP_GPS_MTK19.cpp
+++ b/libraries/AP_GPS/AP_GPS_MTK19.cpp
@@ -230,12 +230,12 @@ AP_GPS_MTK19::_detect(uint8_t data)
 		case 1:
             if ((mtk_type_step1 == MTK_GPS_REVISION_V16) && (PREAMBLE2_V16 == data)){
                 step++;
-				mtk_type_step2  == MTK_GPS_REVISION_V16;
+				mtk_type_step2 = MTK_GPS_REVISION_V16;
                 break;
             }
 			if ((mtk_type_step1 == MTK_GPS_REVISION_V19) && (PREAMBLE2_V19 == data)){
 				step++;
-				mtk_type_step2  == MTK_GPS_REVISION_V19;
+				mtk_type_step2 = MTK_GPS_REVISION_V19;
 				break;
 			}
 			mtk_type_step1 			= 0;
@@ -257,7 +257,7 @@ AP_GPS_MTK19::_detect(uint8_t data)
         case 4:
             step++;
             if (ck_a != data) {
-				Serial.printf("wrong ck_a\n");
+				Serial.print_P(PSTR("wrong ck_a\n"));
                 step 				= 0;
             }
             break;
@@ -266,7 +266,7 @@ AP_GPS_MTK19::_detect(uint8_t data)
             if (ck_b == data) {
 				return true;
             }
-			Serial.printf("wrong ck_b\n");
+			Serial.print_P(PSTR("wrong ck_b\n"));
 			break;
 	}
     return false;