diff --git a/boot/bootutil/src/loader.c b/boot/bootutil/src/loader.c
index 374d140..270b0d6 100644
--- a/boot/bootutil/src/loader.c
+++ b/boot/bootutil/src/loader.c
@@ -129,11 +129,15 @@
  */
 static int
 boot_add_shared_data(struct boot_loader_state *state,
-                     uint32_t active_slot)
+                     uint8_t active_slot)
 {
 #if defined(MCUBOOT_MEASURED_BOOT) || defined(MCUBOOT_DATA_SHARING)
     int rc;
 
+#ifdef MCUBOOT_DATA_SHARING
+    int max_app_size;
+#endif
+
 #ifdef MCUBOOT_MEASURED_BOOT
     rc = boot_save_boot_status(BOOT_CURR_IMG(state),
                                 boot_img_hdr(state, active_slot),
@@ -145,8 +149,10 @@
 #endif /* MCUBOOT_MEASURED_BOOT */
 
 #ifdef MCUBOOT_DATA_SHARING
+    max_app_size = app_max_size(state);
     rc = boot_save_shared_data(boot_img_hdr(state, active_slot),
-                                BOOT_IMG_AREA(state, active_slot));
+                                BOOT_IMG_AREA(state, active_slot),
+                                active_slot, max_app_size);
     if (rc != 0) {
         BOOT_LOG_ERR("Failed to add data to shared memory area.");
         return rc;
@@ -3278,7 +3284,7 @@
             goto out;
         }
 
-        rc = boot_add_shared_data(state, state->slot_usage[BOOT_CURR_IMG(state)].active_slot);
+        rc = boot_add_shared_data(state, (uint8_t)state->slot_usage[BOOT_CURR_IMG(state)].active_slot);
         if (rc != 0) {
             FIH_SET(fih_rc, FIH_FAILURE);
             goto out;
diff --git a/boot/bootutil/src/swap_move.c b/boot/bootutil/src/swap_move.c
index d7b5108..61246b9 100644
--- a/boot/bootutil/src/swap_move.c
+++ b/boot/bootutil/src/swap_move.c
@@ -542,4 +542,26 @@
     flash_area_close(fap_sec);
 }
 
+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);
+}
+
 #endif
diff --git a/boot/bootutil/src/swap_priv.h b/boot/bootutil/src/swap_priv.h
index 86d0b72..960c722 100644
--- a/boot/bootutil/src/swap_priv.h
+++ b/boot/bootutil/src/swap_priv.h
@@ -101,4 +101,9 @@
 
 #endif /* defined(MCUBOOT_SWAP_USING_SCRATCH) || defined(MCUBOOT_SWAP_USING_MOVE) */
 
+/**
+ * Returns the maximum size of an application that can be loaded to a slot.
+ */
+int app_max_size(struct boot_loader_state *state);
+
 #endif /* H_SWAP_PRIV_ */
diff --git a/boot/bootutil/src/swap_scratch.c b/boot/bootutil/src/swap_scratch.c
index bb0d12d..66cbdce 100644
--- a/boot/bootutil/src/swap_scratch.c
+++ b/boot/bootutil/src/swap_scratch.c
@@ -743,6 +743,118 @@
 }
 #endif /* !MCUBOOT_OVERWRITE_ONLY */
 
+int app_max_size(struct boot_loader_state *state)
+{
+    size_t num_sectors_primary;
+    size_t num_sectors_secondary;
+    size_t sz0, sz1;
+    size_t primary_slot_sz, secondary_slot_sz;
+#ifndef MCUBOOT_OVERWRITE_ONLY
+    size_t scratch_sz;
+#endif
+    size_t i, j;
+    int8_t smaller;
+
+    num_sectors_primary = boot_img_num_sectors(state, BOOT_PRIMARY_SLOT);
+    num_sectors_secondary = boot_img_num_sectors(state, BOOT_SECONDARY_SLOT);
+
+#ifndef MCUBOOT_OVERWRITE_ONLY
+    scratch_sz = boot_scratch_area_size(state);
+#endif
+
+    /*
+     * The following loop scans all sectors in a linear fashion, assuring that
+     * for each possible sector in each slot, it is able to fit in the other
+     * slot's sector or sectors. Slot's should be compatible as long as any
+     * number of a slot's sectors are able to fit into another, which only
+     * excludes cases where sector sizes are not a multiple of each other.
+     */
+    i = sz0 = primary_slot_sz = 0;
+    j = sz1 = secondary_slot_sz = 0;
+    smaller = 0;
+    while (i < num_sectors_primary || j < num_sectors_secondary) {
+        if (sz0 == sz1) {
+            sz0 += boot_img_sector_size(state, BOOT_PRIMARY_SLOT, i);
+            sz1 += boot_img_sector_size(state, BOOT_SECONDARY_SLOT, j);
+            i++;
+            j++;
+        } else if (sz0 < sz1) {
+            sz0 += boot_img_sector_size(state, BOOT_PRIMARY_SLOT, i);
+            /* Guarantee that multiple sectors of the secondary slot
+             * fit into the primary slot.
+             */
+            if (smaller == 2) {
+                BOOT_LOG_WRN("Cannot upgrade: slots have non-compatible sectors");
+                return 0;
+            }
+            smaller = 1;
+            i++;
+        } else {
+            sz1 += boot_img_sector_size(state, BOOT_SECONDARY_SLOT, j);
+            /* Guarantee that multiple sectors of the primary slot
+             * fit into the secondary slot.
+             */
+            if (smaller == 1) {
+                BOOT_LOG_WRN("Cannot upgrade: slots have non-compatible sectors");
+                return 0;
+            }
+            smaller = 2;
+            j++;
+        }
+#ifndef MCUBOOT_OVERWRITE_ONLY
+        if (sz0 == sz1) {
+            primary_slot_sz += sz0;
+            secondary_slot_sz += sz1;
+            /* Scratch has to fit each swap operation to the size of the larger
+             * sector among the primary slot and the secondary slot.
+             */
+            if (sz0 > scratch_sz || sz1 > scratch_sz) {
+                BOOT_LOG_WRN("Cannot upgrade: not all sectors fit inside scratch");
+                return 0;
+            }
+            smaller = sz0 = sz1 = 0;
+        }
+#endif
+    }
+
+#ifdef MCUBOOT_OVERWRITE_ONLY
+    return (sz1 < sz0 ? sz1 : sz0);
+#else
+    return (secondary_slot_sz < primary_slot_sz ? secondary_slot_sz : primary_slot_sz);
+#endif
+}
+#else
+int app_max_size(struct boot_loader_state *state)
+{
+    const struct flash_area *fap;
+    int fa_id;
+    int rc;
+    uint32_t active_slot;
+    int primary_sz, secondary_sz;
+
+    active_slot = state->slot_usage[BOOT_CURR_IMG(state)].active_slot;
+
+    fa_id = flash_area_id_from_multi_image_slot(BOOT_CURR_IMG(state), active_slot);
+    rc = flash_area_open(fa_id, &fap);
+    assert(rc == 0);
+    primary_sz = flash_area_get_size(fap);
+    flash_area_close(fap);
+
+    if (active_slot == BOOT_PRIMARY_SLOT) {
+        active_slot = BOOT_SECONDARY_SLOT;
+    } else {
+        active_slot = BOOT_PRIMARY_SLOT;
+    }
+
+    fa_id = flash_area_id_from_multi_image_slot(BOOT_CURR_IMG(state), active_slot);
+    rc = flash_area_open(fa_id, &fap);
+    assert(rc == 0);
+    secondary_sz = flash_area_get_size(fap);
+    flash_area_close(fap);
+
+    return (secondary_sz < primary_sz ? secondary_sz : primary_sz);
+}
+
 #endif /* !MCUBOOT_DIRECT_XIP && !MCUBOOT_RAM_LOAD */
 
 #endif /* !MCUBOOT_SWAP_USING_MOVE */