diff --git a/boot/bootutil/src/swap_move.c b/boot/bootutil/src/swap_move.c
index 61246b9e..111e82f0 100644
--- a/boot/bootutil/src/swap_move.c
+++ b/boot/bootutil/src/swap_move.c
@@ -234,6 +234,28 @@ boot_status_internal_off(const struct boot_status *bs, int elem_sz)
     return off;
 }
 
+static int app_max_sectors(struct boot_loader_state *state)
+{
+    uint32_t sz = 0;
+    uint32_t sector_sz;
+    uint32_t trailer_sz;
+    uint32_t first_trailer_idx;
+
+    sector_sz = boot_img_sector_size(state, BOOT_PRIMARY_SLOT, 0);
+    trailer_sz = boot_trailer_sz(BOOT_WRITE_SZ(state));
+    first_trailer_idx = boot_img_num_sectors(state, BOOT_PRIMARY_SLOT) - 1;
+
+    while (1) {
+        sz += sector_sz;
+        if  (sz >= trailer_sz) {
+            break;
+        }
+        first_trailer_idx--;
+    }
+
+    return first_trailer_idx;
+}
+
 int
 boot_slots_compatible(struct boot_loader_state *state)
 {
@@ -242,18 +264,29 @@ boot_slots_compatible(struct boot_loader_state *state)
     size_t sector_sz_pri = 0;
     size_t sector_sz_sec = 0;
     size_t i;
+    size_t num_usable_sectors_pri;
 
     num_sectors_pri = boot_img_num_sectors(state, BOOT_PRIMARY_SLOT);
     num_sectors_sec = boot_img_num_sectors(state, BOOT_SECONDARY_SLOT);
+    num_usable_sectors_pri = app_max_sectors(state);
+
     if ((num_sectors_pri != num_sectors_sec) &&
-            (num_sectors_pri != (num_sectors_sec + 1))) {
+            (num_sectors_pri != (num_sectors_sec + 1)) &&
+            (num_usable_sectors_pri != (num_sectors_sec + 1))) {
         BOOT_LOG_WRN("Cannot upgrade: not a compatible amount of sectors");
+        BOOT_LOG_DBG("slot0 sectors: %d, slot1 sectors: %d, usable slot0 sectors: %d",
+                     (int)num_sectors_pri, (int)num_sectors_sec,
+                     (int)(num_usable_sectors_pri - 1));
+        return 0;
+    } else if (num_sectors_pri > BOOT_MAX_IMG_SECTORS) {
+        BOOT_LOG_WRN("Cannot upgrade: more sectors than allowed");
         return 0;
     }
 
-    if (num_sectors_pri > BOOT_MAX_IMG_SECTORS) {
-        BOOT_LOG_WRN("Cannot upgrade: more sectors than allowed");
-        return 0;
+    if (num_usable_sectors_pri != (num_sectors_sec + 1)) {
+        BOOT_LOG_DBG("Non-optimal sector distribution, slot0 has %d usable sectors (%d assigned) "
+                     "but slot1 has %d assigned", (int)(num_usable_sectors_pri - 1),
+                     (int)num_sectors_pri, (int)num_sectors_sec);
     }
 
     for (i = 0; i < num_sectors_sec; i++) {
@@ -544,24 +577,11 @@ swap_run(struct boot_loader_state *state, struct boot_status *bs,
 
 int app_max_size(struct boot_loader_state *state)
 {
-    uint32_t sz = 0;
     uint32_t sector_sz;
-    uint32_t trailer_sz;
-    uint32_t first_trailer_idx;
 
     sector_sz = boot_img_sector_size(state, BOOT_PRIMARY_SLOT, 0);
-    trailer_sz = boot_trailer_sz(BOOT_WRITE_SZ(state));
-    first_trailer_idx = boot_img_num_sectors(state, BOOT_PRIMARY_SLOT) - 1;
 
-    while (1) {
-        sz += sector_sz;
-        if  (sz >= trailer_sz) {
-            break;
-        }
-        first_trailer_idx--;
-    }
-
-    return (first_trailer_idx * sector_sz);
+    return (app_max_sectors(state) * sector_sz);
 }
 
 #endif