diff --git a/libraries/AP_Math/vector2.h b/libraries/AP_Math/vector2.h
index fd57b91454b7c..ae43ee847ae74 100644
--- a/libraries/AP_Math/vector2.h
+++ b/libraries/AP_Math/vector2.h
@@ -32,6 +32,9 @@
 #ifndef MATH_CHECK_INDEXES
 #define MATH_CHECK_INDEXES 0
 #endif
+#if MATH_CHECK_INDEXES
+#include <assert.h>
+#endif
 
 #include <cmath>
 #include <float.h>