diff --git a/APMrover2/crash_check.cpp b/APMrover2/crash_check.cpp
index 10360f0c9e..d7b402ebfa 100644
--- a/APMrover2/crash_check.cpp
+++ b/APMrover2/crash_check.cpp
@@ -1,9 +1,9 @@
 #include "Rover.h"
 
 // Code to detect a crash or block
-#define CRASH_CHECK_TRIGGER_SEC     2       // 2 seconds blocked indicates a crash
-#define CRASH_CHECK_THROTTLE_MIN    5.0f    // vehicle must have a throttle greater that 5% to be considered crashed
-#define CRASH_CHECK_VEL_MIN         0.08f   // vehicle must have a velocity under 0.08 m/s or rad/s to be considered crashed
+static const uint16_t CRASH_CHECK_TRIGGER_SEC = 2;   // 2 seconds blocked indicates a crash
+static const float CRASH_CHECK_THROTTLE_MIN = 5.0f;  // vehicle must have a throttle greater that 5% to be considered crashed
+static const float CRASH_CHECK_VEL_MIN = 0.08f;      // vehicle must have a velocity under 0.08 m/s or rad/s to be considered crashed
 
 // crash_check - disarms motors if a crash or block has been detected
 // crashes are detected by the vehicle being static (no speed) for more than CRASH_CHECK_TRIGGER_SEC and motor are running