diff --git a/embassy-stm32/src/flash/asynch.rs b/embassy-stm32/src/flash/asynch.rs
index a0d994956..3c3ece99a 100644
--- a/embassy-stm32/src/flash/asynch.rs
+++ b/embassy-stm32/src/flash/asynch.rs
@@ -34,7 +34,7 @@ impl<'d> Flash<'d, Async> {
     }
 
     pub fn into_regions(self) -> FlashLayout<'d, Async> {
-        family::set_default_layout();
+        assert!(family::is_default_layout());
         FlashLayout::new(self.inner)
     }
 
diff --git a/embassy-stm32/src/flash/common.rs b/embassy-stm32/src/flash/common.rs
index cc0e2572b..6c1912900 100644
--- a/embassy-stm32/src/flash/common.rs
+++ b/embassy-stm32/src/flash/common.rs
@@ -30,7 +30,7 @@ impl<'d> Flash<'d, Blocking> {
 
 impl<'d, MODE> Flash<'d, MODE> {
     pub fn into_blocking_regions(self) -> FlashLayout<'d, Blocking> {
-        family::set_default_layout();
+        assert!(family::is_default_layout());
         FlashLayout::new(self.inner)
     }
 
diff --git a/embassy-stm32/src/flash/f0.rs b/embassy-stm32/src/flash/f0.rs
index e9916d14b..02bd4cc1f 100644
--- a/embassy-stm32/src/flash/f0.rs
+++ b/embassy-stm32/src/flash/f0.rs
@@ -7,7 +7,9 @@ use super::{FlashRegion, FlashSector, FLASH_REGIONS, WRITE_SIZE};
 use crate::flash::Error;
 use crate::pac;
 
-pub const fn set_default_layout() {}
+pub const fn is_default_layout() -> bool {
+    true
+}
 
 pub const fn get_flash_regions() -> &'static [&'static FlashRegion] {
     &FLASH_REGIONS
diff --git a/embassy-stm32/src/flash/f3.rs b/embassy-stm32/src/flash/f3.rs
index 4e65f5580..b093a7837 100644
--- a/embassy-stm32/src/flash/f3.rs
+++ b/embassy-stm32/src/flash/f3.rs
@@ -7,7 +7,9 @@ use super::{FlashRegion, FlashSector, FLASH_REGIONS, WRITE_SIZE};
 use crate::flash::Error;
 use crate::pac;
 
-pub const fn set_default_layout() {}
+pub const fn is_default_layout() -> bool {
+    true
+}
 
 pub const fn get_flash_regions() -> &'static [&'static FlashRegion] {
     &FLASH_REGIONS
diff --git a/embassy-stm32/src/flash/f4.rs b/embassy-stm32/src/flash/f4.rs
index 25d96ca1e..5e1fc696f 100644
--- a/embassy-stm32/src/flash/f4.rs
+++ b/embassy-stm32/src/flash/f4.rs
@@ -69,7 +69,7 @@ mod alt_regions {
 
     impl<'d> Flash<'d> {
         pub fn into_alt_regions(self) -> AltFlashLayout<'d, Async> {
-            super::set_alt_layout();
+            assert!(!super::is_default_layout());
 
             // SAFETY: We never expose the cloned peripheral references, and their instance is not public.
             // Also, all async flash region operations are protected with a mutex.
@@ -86,7 +86,7 @@ mod alt_regions {
         }
 
         pub fn into_alt_blocking_regions(self) -> AltFlashLayout<'d, Blocking> {
-            super::set_alt_layout();
+            assert!(!super::is_default_layout());
 
             // SAFETY: We never expose the cloned peripheral references, and their instance is not public.
             // Also, all blocking flash region operations are protected with a cs.
@@ -191,38 +191,21 @@ impl FlashSector {
 }
 
 #[cfg(any(stm32f427, stm32f429, stm32f437, stm32f439, stm32f469, stm32f479))]
-pub fn set_default_layout() {
-    unsafe {
-        pac::FLASH.optkeyr().write(|w| w.set_optkey(0x08192A3B));
-        pac::FLASH.optkeyr().write(|w| w.set_optkey(0x4C5D6E7F));
-        pac::FLASH.optcr().modify(|r| {
-            r.set_db1m(false);
-            r.set_optlock(true)
-        });
-    };
+pub(crate) fn is_default_layout() -> bool {
+    unsafe { !pac::FLASH.optcr().read().db1m() }
 }
 
 #[cfg(not(any(stm32f427, stm32f429, stm32f437, stm32f439, stm32f469, stm32f479)))]
-pub const fn set_default_layout() {}
-
-#[cfg(any(stm32f427, stm32f429, stm32f437, stm32f439, stm32f469, stm32f479))]
-fn set_alt_layout() {
-    unsafe {
-        pac::FLASH.optkeyr().write(|w| w.set_optkey(0x08192A3B));
-        pac::FLASH.optkeyr().write(|w| w.set_optkey(0x4C5D6E7F));
-        pac::FLASH.optcr().modify(|r| {
-            r.set_db1m(true);
-            r.set_optlock(true)
-        });
-    };
+pub(crate) const fn is_default_layout() -> bool {
+    true
 }
 
 #[cfg(any(stm32f427, stm32f429, stm32f437, stm32f439, stm32f469, stm32f479))]
 pub fn get_flash_regions() -> &'static [&'static FlashRegion] {
-    if unsafe { pac::FLASH.optcr().read().db1m() } {
-        &ALT_FLASH_REGIONS
-    } else {
+    if is_default_layout() {
         &FLASH_REGIONS
+    } else {
+        &ALT_FLASH_REGIONS
     }
 }
 
diff --git a/embassy-stm32/src/flash/f7.rs b/embassy-stm32/src/flash/f7.rs
index e6267e178..1a6d6bb03 100644
--- a/embassy-stm32/src/flash/f7.rs
+++ b/embassy-stm32/src/flash/f7.rs
@@ -6,7 +6,9 @@ use super::{FlashRegion, FlashSector, FLASH_REGIONS, WRITE_SIZE};
 use crate::flash::Error;
 use crate::pac;
 
-pub const fn set_default_layout() {}
+pub const fn is_default_layout() -> bool {
+    true
+}
 
 pub const fn get_flash_regions() -> &'static [&'static FlashRegion] {
     &FLASH_REGIONS
diff --git a/embassy-stm32/src/flash/h7.rs b/embassy-stm32/src/flash/h7.rs
index d09ebc0dd..9baf059ee 100644
--- a/embassy-stm32/src/flash/h7.rs
+++ b/embassy-stm32/src/flash/h7.rs
@@ -7,7 +7,9 @@ use super::{FlashRegion, FlashSector, BANK1_REGION, FLASH_REGIONS, WRITE_SIZE};
 use crate::flash::Error;
 use crate::pac;
 
-pub const fn set_default_layout() {}
+pub const fn is_default_layout() -> bool {
+    true
+}
 
 const fn is_dual_bank() -> bool {
     FLASH_REGIONS.len() == 2
diff --git a/embassy-stm32/src/flash/l.rs b/embassy-stm32/src/flash/l.rs
index c4bbd5477..deefd05ed 100644
--- a/embassy-stm32/src/flash/l.rs
+++ b/embassy-stm32/src/flash/l.rs
@@ -6,7 +6,9 @@ use super::{FlashRegion, FlashSector, FLASH_REGIONS, WRITE_SIZE};
 use crate::flash::Error;
 use crate::pac;
 
-pub const fn set_default_layout() {}
+pub const fn is_default_layout() -> bool {
+    true
+}
 
 pub const fn get_flash_regions() -> &'static [&'static FlashRegion] {
     &FLASH_REGIONS
diff --git a/embassy-stm32/src/flash/other.rs b/embassy-stm32/src/flash/other.rs
index ccdcfeb7a..a7e8d1d57 100644
--- a/embassy-stm32/src/flash/other.rs
+++ b/embassy-stm32/src/flash/other.rs
@@ -2,7 +2,9 @@
 
 use super::{Error, FlashRegion, FlashSector, FLASH_REGIONS, WRITE_SIZE};
 
-pub const fn set_default_layout() {}
+pub const fn is_default_layout() -> bool {
+    true
+}
 
 pub const fn get_flash_regions() -> &'static [&'static FlashRegion] {
     &FLASH_REGIONS