diff --git a/include/apple2.dd.h b/include/apple2.dd.h
index d89a063..0fefb80 100644
--- a/include/apple2.dd.h
+++ b/include/apple2.dd.h
@@ -185,15 +185,16 @@ struct apple2dd {
 extern SEGMENT_READER(apple2_dd_switch_read);
 extern SEGMENT_WRITER(apple2_dd_switch_write);
 extern apple2dd *apple2_dd_create();
+extern int apple2_dd_decode(apple2dd *);
+extern int apple2_dd_encode(apple2dd *);
 extern int apple2_dd_insert(apple2dd *, FILE *, int);
 extern int apple2_dd_position(apple2dd *);
 extern vm_8bit apple2_dd_read(apple2dd *);
 extern vm_8bit apple2_dd_switch_rw(apple2dd *);
 extern void apple2_dd_eject(apple2dd *);
-extern void apple2_dd_encode(apple2dd *);
-extern void apple2_dd_decode(apple2dd *);
 extern void apple2_dd_free(apple2dd *);
 extern void apple2_dd_map(vm_segment *);
+extern void apple2_dd_save(apple2dd *);
 extern void apple2_dd_set_mode(apple2dd *, int);
 extern void apple2_dd_shift(apple2dd *, int);
 extern void apple2_dd_step(apple2dd *, int);
@@ -203,6 +204,5 @@ extern void apple2_dd_switch_phase(apple2dd *, size_t);
 extern void apple2_dd_turn_on(apple2dd *, bool);
 extern void apple2_dd_write(apple2dd *);
 extern void apple2_dd_write_protect(apple2dd *, bool);
-extern void apple2_dd_save(apple2dd *);
 
 #endif
diff --git a/src/apple2.dd.c b/src/apple2.dd.c
index c71745f..27763bf 100644
--- a/src/apple2.dd.c
+++ b/src/apple2.dd.c
@@ -97,7 +97,7 @@ apple2_dd_insert(apple2dd *drive, FILE *stream, int type)
  * 6-and-2 encoding, if necessary. (It is not necessary if the
  * image_type is DD_NIBBLE.)
  */
-void
+int
 apple2_dd_encode(apple2dd *drive)
 {
     switch (drive->image_type) {
@@ -112,8 +112,10 @@ apple2_dd_encode(apple2dd *drive)
 
         default:
             log_critical("Unknown image type");
-            exit(1);
+            return ERR_INVALID;
     }
+
+    return OK;
 }
 
 /*
@@ -138,7 +140,7 @@ apple2_dd_save(apple2dd *drive)
  * the 6-and-2 encoding (if need be -- see note on DD_NIBBLE for the
  * encode function).
  */
-void
+int
 apple2_dd_decode(apple2dd *drive)
 {
     switch (drive->image_type) {
@@ -153,8 +155,10 @@ apple2_dd_decode(apple2dd *drive)
 
         default:
             log_critical("Unknown image type");
-            exit(1);
+            return ERR_INVALID;
     }
+
+    return OK;
 }
 
 /*