__forceinline causing Error L6218E?

Using Keil MCBSTM32 (STM32F103RB processor) and uVision3 V3.55a

The goal is to "encapsulate" data in C. To do this I want to create access methods (get/put) that are accessible externally, but the data, being declared static, is not.

I also want to appease those who want faster code so I was attempting to "inline" the methods.

The test code is as follows:

#include counter.h
static unsigned int counter;

/**
 Method to get counter.
*/
__forceinline unsigned int get_counter()
{
        return counter;
}

/**
 Method to set counter.
*/
__forceinline void put_counter( unsigned int val)
{
        counter = val;
}

The counter.h contains the following:

__forceinline unsigned int get_counter(void);
__forceinline void put_counter( unsigned int val);

(Note: tried the declarations in the .h file with and without the __forceinline)

The main() contains:

static unsigned int opt_test;

/*----------------------------------------------------------------------------
  MAIN function
 *----------------------------------------------------------------------------*/
int main (void) {


  stm32_Init ();                                  // STM32 setup

  GPIOB->ODR |=  (1 << (ledPos+8));               // switch on initial LED position

  while (1) {                                     // Loop forever

        opt_test = get_counter();
        opt_test++;
        put_counter( opt_test );

  } // end while

(Note: this was just tacked onto the "Timer" project to try things out)

What I get:

Build target 'MCBSTM32'
assembling STM32F10x.s...
creating preprocessor file for STM32_Init.c...
compiling STM32_Init.c...
creating preprocessor file for Timer.c...
compiling Timer.c...
creating preprocessor file for optimize.c...
compiling optimize.c...
linking...
.\Obj\Timer.axf: Error: L6218E: Undefined symbol get_counter (referred from timer.o).
.\Obj\Timer.axf: Error: L6218E: Undefined symbol put_counter (referred from timer.o).
Target not created

What I have tried: Compiled with optimization levels of 2 and 3.

Is this functionality actually working? If so, is there anything I should be looking out for that might cause this error?