diff --git a/ion/src/device/bootloader/drivers/external_flash.cpp b/ion/src/device/bootloader/drivers/external_flash.cpp
index 1c7686cd4..612efc017 100644
--- a/ion/src/device/bootloader/drivers/external_flash.cpp
+++ b/ion/src/device/bootloader/drivers/external_flash.cpp
@@ -405,7 +405,7 @@ int SectorAtAddress(uint32_t address) {
   i = address >> NumberOfAddressBitsIn32KbyteBlock;
   if (i >= 1) {
     i = Config::NumberOf4KSectors + i - 1;
-    assert(i >= 0 && i <= Config::NumberOf32KSectors);
+    assert(i >= Config::NumberOf4KSectors && i <= Config::NumberOf4KSectors + Config::NumberOf32KSectors);
     return i;
   }
   i = address >> NumberOfAddressBitsIn4KbyteBlock;