diff --git a/include/apple2.dd.h b/include/apple2.dd.h
index 26d7734..ed799e7 100644
--- a/include/apple2.dd.h
+++ b/include/apple2.dd.h
@@ -189,6 +189,7 @@ 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 int apple2_dd_sector_num(int, int);
 extern vm_8bit apple2_dd_read(apple2dd *);
 extern vm_8bit apple2_dd_switch_rw(apple2dd *);
 extern void apple2_dd_eject(apple2dd *);
diff --git a/include/apple2.enc.h b/include/apple2.enc.h
index 61ec499..9d41925 100644
--- a/include/apple2.enc.h
+++ b/include/apple2.enc.h
@@ -62,8 +62,8 @@
 extern int apple2_enc_4n4(vm_segment *, int, vm_8bit); 
 extern int apple2_enc_sector(vm_segment *, vm_segment *, int, int);
 extern int apple2_enc_sector_header(vm_segment *, int, int, int);
-extern int apple2_enc_track(vm_segment *, vm_segment *, const int *, int, int);
-extern vm_segment *apple2_enc_dos(vm_segment *, const int *);
+extern int apple2_enc_track(int, vm_segment *, vm_segment *, int, int);
+extern vm_segment *apple2_enc_dos(int, vm_segment *);
 extern vm_segment *apple2_enc_nib(vm_segment *);
 
 #endif
diff --git a/src/apple2.dd.c b/src/apple2.dd.c
index 97054ea..62a8dbd 100644
--- a/src/apple2.dd.c
+++ b/src/apple2.dd.c
@@ -14,16 +14,6 @@
 #include "apple2.enc.h"
 #include "apple2.h"
 
-static int sector_dos33[] = {
-    0x0, 0x7, 0xe, 0x6, 0xd, 0x5, 0xc, 0x4,
-    0xb, 0x3, 0xa, 0x2, 0x9, 0x1, 0x8, 0xf,
-};
-
-static int sector_prodos[] = {
-    0x0, 0x8, 0x1, 0x9, 0x2, 0xa, 0x3, 0xb,
-    0x4, 0xc, 0x5, 0xd, 0x6, 0xe, 0x7, 0xf,
-};
-
 /*
  * Create a new disk drive. We do not create a memory segment for the
  * drive right away, as the size of said data can be variable based on
@@ -59,6 +49,42 @@ apple2_dd_create()
     return drive;
 }
 
+int
+apple2_dd_sector_num(int type, int sect)
+{
+    static const int dos33[] = {
+        0x0, 0x7, 0xe, 0x6, 0xd, 0x5, 0xc, 0x4,
+        0xb, 0x3, 0xa, 0x2, 0x9, 0x1, 0x8, 0xf,
+    };
+
+    static const int prodos[] = {
+        0x0, 0x8, 0x1, 0x9, 0x2, 0xa, 0x3, 0xb,
+        0x4, 0xc, 0x5, 0xd, 0x6, 0xe, 0x7, 0xf,
+    };
+
+    const int *sectab;
+
+    // Booooo
+    if (sect < 0 || sect > 15) {
+        return 0;
+    }
+
+    switch (type) {
+        case DD_DOS33:
+            sectab = dos33;
+            break;
+            
+        case DD_PRODOS:
+            sectab = prodos;
+            break;
+
+        case DD_NIBBLE:
+            return sect;
+    }
+
+    return sectab[sect];
+}
+
 /*
  * Insert a "disk" into the drive, such that a disk is delivered to us
  * through a FILE stream. Return an error code if the disk format is
@@ -123,11 +149,8 @@ apple2_dd_encode(apple2dd *drive)
             break;
 
         case DD_DOS33:
-            drive->data = apple2_enc_dos(drive->image, sector_dos33);
-            break;
-
         case DD_PRODOS:
-            drive->data = apple2_enc_dos(drive->image, sector_prodos);
+            drive->data = apple2_enc_dos(drive->image_type, drive->image);
             break;
 
         default:
diff --git a/src/apple2.enc.c b/src/apple2.enc.c
index ba479d6..08fe44e 100644
--- a/src/apple2.enc.c
+++ b/src/apple2.enc.c
@@ -39,7 +39,7 @@ static vm_8bit gcr62[] = {
  * 3.2 and 3.1 (which use 5-and-3 encoding).
  */
 vm_segment *
-apple2_enc_dos(vm_segment *src, const int *sectab)
+apple2_enc_dos(int type, vm_segment *src)
 {
     vm_segment *dest;
     int i, doff = 0;
@@ -58,7 +58,7 @@ apple2_enc_dos(vm_segment *src, const int *sectab)
     // away with just using tracks-and-sectors. In particular, DOS 3.3
     // has 35 tracks of 4096 bytes each.
     for (i = 0; i < 35; i++) {
-        doff += apple2_enc_track(dest, src, sectab, doff, i);
+        doff += apple2_enc_track(type, dest, src, doff, i);
     }
 
     return dest;
@@ -105,7 +105,7 @@ apple2_enc_nib(vm_segment *src)
  * written into dest.
  */
 int
-apple2_enc_track(vm_segment *dest, vm_segment *src, const int *sectab,
+apple2_enc_track(int sectype, vm_segment *dest, vm_segment *src,
                  int doff, int track)
 {
     int toff = track * ENC_DTRACK;
@@ -119,7 +119,7 @@ apple2_enc_track(vm_segment *dest, vm_segment *src, const int *sectab,
     }
 
     for (sect = 0; sect < 16; sect++) {
-        soff = toff + (ENC_DSECTOR * sectab[sect]);
+        soff = toff + (ENC_DSECTOR * apple2_dd_sector_num(sectype, sect));
 
         // Each sector has a header with some metadata, plus some
         // markers and padding.
diff --git a/tests/apple2.dd.c b/tests/apple2.dd.c
index f68acac..ae72638 100644
--- a/tests/apple2.dd.c
+++ b/tests/apple2.dd.c
@@ -323,3 +323,20 @@ Test(apple2_dd, map)
 
     vm_segment_free(seg);
 }
+
+Test(apple2_dd, sector_num)
+{
+    static const int dos33[] = {
+        0x0, 0x7, 0xe, 0x6, 0xd, 0x5, 0xc, 0x4,
+        0xb, 0x3, 0xa, 0x2, 0x9, 0x1, 0x8, 0xf,
+    };
+
+    static const int prodos[] = {
+        0x0, 0x8, 0x1, 0x9, 0x2, 0xa, 0x3, 0xb,
+        0x4, 0xc, 0x5, 0xd, 0x6, 0xe, 0x7, 0xf,
+    };
+
+    for (int i = 0; i < 16; i++) {
+        cr_assert_eq(apple2_dd_sector_num(DD_DOS33, i), dos33[i]);
+    }
+}
diff --git a/tests/apple2.enc.c b/tests/apple2.enc.c
index 20d6bf1..4e475f4 100644
--- a/tests/apple2.enc.c
+++ b/tests/apple2.enc.c
@@ -93,7 +93,7 @@ Test(apple2_enc, dos)
     FILE *fp = fopen("../../build/karateka.dsk", "r");
 
     vm_segment_fread(seg, fp, 0, _140K_);
-    enc = apple2_enc_dos(seg, sectab);
+    enc = apple2_enc_dos(DD_DOS33, seg);
 
     cr_assert_neq(enc, NULL);
 
@@ -197,7 +197,7 @@ Test(apple2_enc, track)
         vm_segment_copy_buf(seg, f_sector, i * ENC_DSECTOR, 0, 256);
     }
 
-    apple2_enc_track(dest, seg, sectab, 0, 0);
+    apple2_enc_track(DD_DOS33, dest, seg, 0, 0);
 
     for (i = 0; i < ENC_ETRACK_HEADER; i++) {
         cr_assert_eq(vm_segment_get(dest, i), 0xff);