diff --git a/boot/bootutil/src/swap_move.c b/boot/bootutil/src/swap_move.c
index 9901bc62..8999403c 100644
--- a/boot/bootutil/src/swap_move.c
+++ b/boot/bootutil/src/swap_move.c
@@ -577,11 +577,19 @@ swap_run(struct boot_loader_state *state, struct boot_status *bs,
 
 int app_max_size(struct boot_loader_state *state)
 {
-    uint32_t sector_sz;
+    uint32_t sector_sz_primary;
+    uint32_t sector_sz_secondary;
+    uint32_t sz_primary;
+    uint32_t sz_secondary;
 
-    sector_sz = boot_img_sector_size(state, BOOT_PRIMARY_SLOT, 0);
+    sector_sz_primary = boot_img_sector_size(state, BOOT_PRIMARY_SLOT, 0);
+    sector_sz_secondary = boot_img_sector_size(state, BOOT_SECONDARY_SLOT, 0);
 
-    return (app_max_sectors(state) * sector_sz);
+    /* Account for image flags and move sector */
+    sz_primary = app_max_sectors(state) * sector_sz_primary - sector_sz_primary;
+    sz_secondary = boot_img_num_sectors(state, BOOT_SECONDARY_SLOT) * sector_sz_secondary;
+
+    return (sz_primary <= sz_secondary ? sz_primary : sz_secondary);
 }
 
 #endif