diff --git a/Makefile b/Makefile
index 745f9f8..a4e6916 100644
--- a/Makefile
+++ b/Makefile
@@ -131,6 +131,7 @@ C_INCLUDES =  \
 ASFLAGS = $(MCU) $(AS_INCLUDES) $(OPT) -Wall -fdata-sections -ffunction-sections
 
 CFLAGS = $(MCU) $(C_INCLUDES) $(OPT) -Wall -fdata-sections -ffunction-sections
+CFLAGS += -Werror=implicit-function-declaration
 
 ifeq ($(DEBUG), 1)
 CFLAGS += -g -gdwarf-2 -DDEBUG=$(DEBUG)
diff --git a/src/animation.h b/src/animation.h
index cd8ea8e..f5eb48e 100644
--- a/src/animation.h
+++ b/src/animation.h
@@ -18,15 +18,15 @@ void ani_shift_y(bm_t *bm, uint16_t *fb, int dir, int frame);
 void ani_scroll_x(bm_t *bm, uint16_t *fb, int dir);
 void ani_scroll_y(bm_t *bm, uint16_t *fb);
 
-void ani_scroll_left(bm_t *bm, uint16_t *fb);
-void ani_scroll_right(bm_t *bm, uint16_t *fb);
-void ani_scroll_up(bm_t *bm, uint16_t *fb);
-void ani_scroll_down(bm_t *bm, uint16_t *fb);
-void ani_fixed(bm_t *bm, uint16_t *fb);
-void ani_laser(bm_t *bm, uint16_t *fb);
-void ani_snowflake(bm_t *bm, uint16_t *fb);
-void ani_animation(bm_t *bm, uint16_t *fb);
-void ani_picture(bm_t *bm, uint16_t *fb);
+int ani_scroll_left(bm_t *bm, uint16_t *fb);
+int ani_scroll_right(bm_t *bm, uint16_t *fb);
+int ani_scroll_up(bm_t *bm, uint16_t *fb);
+int ani_scroll_down(bm_t *bm, uint16_t *fb);
+int ani_fixed(bm_t *bm, uint16_t *fb);
+int ani_laser(bm_t *bm, uint16_t *fb);
+int ani_snowflake(bm_t *bm, uint16_t *fb);
+int ani_animation(bm_t *bm, uint16_t *fb);
+int ani_picture(bm_t *bm, uint16_t *fb);
 
 void ani_marque(bm_t *bm, uint16_t *fb, int step);
 void ani_flash(bm_t *bm, uint16_t *fb, int step);