double time_average, time_stddev;
        unsigned int bit, i, j;
        unsigned int set_bits, skip;
-       unsigned int old;
 
        init_stats(&fb_time_stats);
        init_stats(&tb_time_stats);
                        __set_bit(i, to_test);
 
                for (i = 0; i < outer_iterations; i++) {
-                       old = accumulator;
+#ifndef NDEBUG
+                       unsigned int old = accumulator;
+#endif
+
                        gettimeofday(&start, NULL);
                        for (j = 0; j < inner_iterations; j++) {
                                for_each_set_bit(bit, to_test, num_bits)
                        runtime_us = diff.tv_sec * USEC_PER_SEC + diff.tv_usec;
                        update_stats(&fb_time_stats, runtime_us);
 
+#ifndef NDEBUG
                        old = accumulator;
+#endif
                        gettimeofday(&start, NULL);
                        for (j = 0; j < inner_iterations; j++) {
                                for (bit = 0; bit < num_bits; bit++) {