Undefined symbols for CMMotionManager

Question

I have an older iOS project and am attempting to add core motion to it. I get this error after adding this line:

self.motionManager = [[CMMotionManager alloc]init];

error:

Undefined symbols for architecture armv7:

"_OBJC_CLASS_$_CMMotionManager", referenced from:

I also got this error when including the i386 architecture. I have now removed all architectures except arm6, but still get this error.

motionManager is declared here:

@property (nonatomic, retain) CMMotionManager * motionManager;

I have the CoreMotion framework included.