diff --git a/libraries/AP_Common/tests/test_expandingstring_failure.cpp b/libraries/AP_Common/tests/test_expandingstring_failure.cpp
index f95d3d9210..98702789f4 100644
--- a/libraries/AP_Common/tests/test_expandingstring_failure.cpp
+++ b/libraries/AP_Common/tests/test_expandingstring_failure.cpp
@@ -47,7 +47,7 @@ public:
     const size_t _size;
 
     uint32_t available() override { return 0; }
-    int16_t read() override { return -1; }
+    bool read(uint8_t &b) override { return false; }
     uint32_t txspace() override { return 0; }
     bool discard_input() override { return false; }
 };
diff --git a/libraries/AP_Common/tests/test_nmea_print.cpp b/libraries/AP_Common/tests/test_nmea_print.cpp
index 85bc0a886d..58e232804f 100644
--- a/libraries/AP_Common/tests/test_nmea_print.cpp
+++ b/libraries/AP_Common/tests/test_nmea_print.cpp
@@ -15,7 +15,7 @@ public:
     bool tx_pending() override { return false; };
     uint32_t available() override { return 1; };
     uint32_t txspace() override { return _txspace; };
-    int16_t read() override { return 1; };
+    bool read(uint8_t &c) override { return false; };
 
     bool discard_input() override { return true; };
     size_t write(uint8_t c) override { return 1; };
diff --git a/libraries/AP_Common/tests/test_nmea_vaprint.cpp b/libraries/AP_Common/tests/test_nmea_vaprint.cpp
index 3df9f06063..ba719234a5 100644
--- a/libraries/AP_Common/tests/test_nmea_vaprint.cpp
+++ b/libraries/AP_Common/tests/test_nmea_vaprint.cpp
@@ -26,7 +26,7 @@ public:
     const size_t _size;
 
     uint32_t available() override { return 0; }
-    int16_t read() override { return -1; }
+    bool read(uint8_t &c) override { return false; };
     uint32_t txspace() override { return 0; }
     bool discard_input() override { return false; }
 };
@@ -53,7 +53,7 @@ public:
     bool tx_pending() override { return false; };
     uint32_t available() override { return 1; };
     uint32_t txspace() override { return _txspace; };
-    int16_t read() override { return 1; };
+    bool read(uint8_t &c) override { return false; };
 
     bool discard_input() override { return true; };
     size_t write(uint8_t c) override { return 1; };