diff --git a/src/oldies.c b/src/oldies.c
index 8c72e212..16c3f9c7 100644
--- a/src/oldies.c
+++ b/src/oldies.c
@@ -27,6 +27,7 @@
 #include <stdlib.h>
 #include <math.h>
 #include "struct.h"
+#include "oldies.h"
 #include "global.h"
 #include "errors.h"
 #include "misc.h"
@@ -35,12 +36,12 @@
 #include "windows.h"
 #include "layers.h"
 
-void Pixel_in_layer(word x,word y, byte layer, byte color)
+static void Set_Pixel_in_layer(word x,word y, byte layer, byte color)
 {
   *((y)*Main.image_width+(x)+Main.backups->Pages->Image[layer].Pixels)=color;
 }
 
-byte C64_FLI(byte *bitmap, byte *screen_ram, byte *color_ram, byte *background)
+int C64_FLI(byte *bitmap, byte *screen_ram, byte *color_ram, byte *background)
 {
   word used_colors[200][40];
   word block_used_colors[25][40];
@@ -346,7 +347,7 @@ byte C64_FLI(byte *bitmap, byte *screen_ram, byte *color_ram, byte *background)
 
 }
 
-byte C64_FLI_enforcer(void)
+int C64_FLI_enforcer(void)
 {
   byte background[200];
   byte bitmap[8000];
@@ -357,12 +358,15 @@ byte C64_FLI_enforcer(void)
   byte c[4];
   
   // Checks
-  if (Main.image_width != 160)
+  if (Main.image_width != 160 || Main.image_height != 200)
+  {
+    GFX2_Log(GFX2_WARNING, "C64_FLI_enforcer() requires 160x200 image resolution\n");
     return 1;
-  if (Main.image_height != 200)
-    return 1;
-  if (Main.backups->Pages->Nb_layers != 4)
+  }
+  if (Main.backups->Pages->Nb_layers != 4) {
+    GFX2_Log(GFX2_WARNING, "C64_FLI_enforcer() requires 4 layers\n");
     return 2;
+  }
   
   Backup_layers(3);
   
@@ -388,7 +392,7 @@ byte C64_FLI_enforcer(void)
         {
           int color=c[(pixel&3)];
           pixel>>=2;
-          Pixel_in_layer(col*4+(3-x),row*8+y,3,color);
+          Set_Pixel_in_layer(col*4+(3-x),row*8+y,3,color);
         }
       }
     }
diff --git a/src/oldies.h b/src/oldies.h
index 6f781883..811fdf7d 100644
--- a/src/oldies.h
+++ b/src/oldies.h
@@ -18,7 +18,19 @@
     along with Grafx2; if not, see <http://www.gnu.org/licenses/>
 */
 
-byte C64_FLI(byte *bitmap, byte *screen_ram, byte *color_ram, byte *background);
+///@file oldies.h
+/// C64 FLI functions
 
-byte C64_FLI_enforcer(void);
+/**
+ * Save a 3 layer picture to C64 FLI format
+ *
+ * @param bitmap a 8000 byte buffer to store bitmap data
+ * @param screen_ram a 8192 byte buffer to store the 8 screen RAMs
+ * @param color_ram a 1000 byte buffer to store the color RAM
+ * @param background a 200 byte buffer to store the background colors
+ * @return 0 for success, 1 if the picture is less than 3 layers, 2 if the picture dimensions are not 160x200
+ */
+int C64_FLI(byte *bitmap, byte *screen_ram, byte *color_ram, byte *background);
+
+int C64_FLI_enforcer(void);