diff --git a/src/mesa/state_tracker/st_program.h b/src/mesa/state_tracker/st_program.h
index 286fabc0117..7483450eae5 100644
--- a/src/mesa/state_tracker/st_program.h
+++ b/src/mesa/state_tracker/st_program.h
@@ -137,7 +137,7 @@ struct st_fp_variant_key
    GLuint lower_two_sided_color:1;
 
    GLuint lower_flatshade:1;
-   enum compare_func lower_alpha_func:3;
+   unsigned lower_alpha_func:3;
 
    /** needed for ATI_fragment_shader */
    char texture_targets[MAX_NUM_FRAGMENT_REGISTERS_ATI];