diff --git a/libraries/AP_InertialSensor/AP_InertialSensor.cpp b/libraries/AP_InertialSensor/AP_InertialSensor.cpp
index 163af7e6a2..d1bbac8333 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor.cpp
+++ b/libraries/AP_InertialSensor/AP_InertialSensor.cpp
@@ -419,7 +419,7 @@ bool AP_InertialSensor::calibrate_accel(AP_InertialSensor_UserInteract* interact
                 PSTR("Place vehicle %S and press any key.\n"), msg);
 
         // wait for user input
-        if (interact->blocking_read()) {
+        if (!interact->blocking_read()) {
             //No need to use interact->printf_P for an error, blocking_read does this when it fails
             goto failed;
         }
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract.h b/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract.h
index f72eeffb4b..baf2d95284 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract.h
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract.h
@@ -7,7 +7,7 @@
 /* Pure virtual interface class */
 class AP_InertialSensor_UserInteract {
 public:
-    virtual uint8_t blocking_read() = 0;
+    virtual bool blocking_read() = 0;
     virtual void _printf_P(const prog_char *, ...) = 0;
 };
 
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_MAVLink.cpp b/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_MAVLink.cpp
index 06e3c2ea36..ce7bdf9117 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_MAVLink.cpp
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_MAVLink.cpp
@@ -7,7 +7,7 @@
 
 extern const AP_HAL::HAL& hal;
 
-uint8_t AP_InertialSensor_UserInteract_MAVLink::blocking_read(void) 
+bool AP_InertialSensor_UserInteract_MAVLink::blocking_read(void) 
 {
     uint32_t start_ms = hal.scheduler->millis();
     /* Wait for a COMMAND_ACK message to be received from the ground station */
@@ -20,12 +20,12 @@ uint8_t AP_InertialSensor_UserInteract_MAVLink::blocking_read(void)
         mavlink_status_t status;
         if (mavlink_parse_char(_chan, c, &msg, &status)) {
             if (msg.msgid == MAVLINK_MSG_ID_COMMAND_ACK) {
-                return 0;
+                return true;
             }
         }
     }
     hal.console->println_P(PSTR("Timed out waiting for user response"));
-    return 1;
+    return false;
 }
 
 void AP_InertialSensor_UserInteract_MAVLink::_printf_P(const prog_char* fmt, ...) 
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_MAVLink.h b/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_MAVLink.h
index 89fb07ea52..4fa3cb4ebf 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_MAVLink.h
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_MAVLink.h
@@ -14,7 +14,7 @@ public:
     AP_InertialSensor_UserInteract_MAVLink(mavlink_channel_t chan) :
         _chan(chan) {}
 
-    uint8_t blocking_read();
+    bool blocking_read();
     void _printf_P(const prog_char *, ...);
 private:
     mavlink_channel_t _chan;
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_Stream.cpp b/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_Stream.cpp
index 35e5a245cf..9aaf53c995 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_Stream.cpp
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_Stream.cpp
@@ -4,7 +4,8 @@
 
 extern const AP_HAL::HAL& hal;
 
-uint8_t AP_InertialSensor_UserInteractStream::blocking_read() {
+bool AP_InertialSensor_UserInteractStream::blocking_read() 
+{
     /* Wait for input to be available */
     while(!_s->available()) {
         hal.scheduler->delay(20);
@@ -15,7 +16,7 @@ uint8_t AP_InertialSensor_UserInteractStream::blocking_read() {
     while (_s->available()) {
         _s->read();
     }
-    return ret;
+    return true;
 }
 
 void AP_InertialSensor_UserInteractStream::_printf_P(
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_Stream.h b/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_Stream.h
index c645df2e11..d445846ef5 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_Stream.h
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_UserInteract_Stream.h
@@ -14,7 +14,7 @@ public:
     AP_InertialSensor_UserInteractStream(AP_HAL::BetterStream *s) :
         _s(s) {}
 
-    uint8_t blocking_read();
+    bool blocking_read();
     void _printf_P(const prog_char *, ...);
 private:
     AP_HAL::BetterStream *_s;