diff --git a/sim/Cargo.lock b/sim/Cargo.lock
index 36f63c8..857adff 100644
--- a/sim/Cargo.lock
+++ b/sim/Cargo.lock
@@ -56,8 +56,8 @@
  "pem 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand 0.3.18 (registry+https://github.com/rust-lang/crates.io-index)",
  "ring 0.12.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.23 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_derive 1.0.23 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.24 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.24 (registry+https://github.com/rust-lang/crates.io-index)",
  "simflash 0.1.0",
  "untrusted 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -102,8 +102,8 @@
 dependencies = [
  "lazy_static 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "regex 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.23 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_derive 1.0.23 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.24 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.24 (registry+https://github.com/rust-lang/crates.io-index)",
  "strsim 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -165,6 +165,11 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
+name = "lazy_static"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
 name = "libc"
 version = "0.2.34"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -254,7 +259,7 @@
  "aho-corasick 0.6.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "memchr 2.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "regex-syntax 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "thread_local 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "thread_local 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "utf8-ranges 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -292,22 +297,22 @@
 
 [[package]]
 name = "serde"
-version = "1.0.23"
+version = "1.0.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "serde_derive"
-version = "1.0.23"
+version = "1.0.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "quote 0.3.15 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_derive_internals 0.17.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive_internals 0.18.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "syn 0.11.11 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "serde_derive_internals"
-version = "0.17.0"
+version = "0.18.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "syn 0.11.11 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -320,7 +325,7 @@
 dependencies = [
  "error-chain 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "rand 0.3.15 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.3.18 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -348,10 +353,10 @@
 
 [[package]]
 name = "thread_local"
-version = "0.3.4"
+version = "0.3.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "lazy_static 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "lazy_static 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "unreachable 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -413,6 +418,7 @@
 "checksum gcc 0.3.54 (registry+https://github.com/rust-lang/crates.io-index)" = "5e33ec290da0d127825013597dbdfc28bee4964690c7ce1166cbc2a7bd08b1bb"
 "checksum kernel32-sys 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "7507624b29483431c0ba2d82aece8ca6cdba9382bff4ddd0f7490560c056098d"
 "checksum lazy_static 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)" = "76f033c7ad61445c5b347c7382dd1237847eb1bce590fe50365dcb33d546be73"
+"checksum lazy_static 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "c8f31047daa365f19be14b47c29df4f7c3b581832407daabe6ae77397619237d"
 "checksum libc 0.2.34 (registry+https://github.com/rust-lang/crates.io-index)" = "36fbc8a8929c632868295d0178dd8f63fc423fd7537ad0738372bd010b3ac9b0"
 "checksum log 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)" = "880f77541efa6e5cc74e76910c9884d9859683118839d6a1dc3b11e63512565b"
 "checksum memchr 2.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "796fba70e76612589ed2ce7f45282f5af869e0fdd7cc6199fa1aa1f1d591ba9d"
@@ -428,13 +434,13 @@
 "checksum rustc-demangle 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "aee45432acc62f7b9a108cc054142dac51f979e69e71ddce7d6fc7adf29e817e"
 "checksum safemem 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e27a8b19b835f7aea908818e871f5cc3a5a186550c30773be987e155e8163d8f"
 "checksum scopeguard 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "94258f53601af11e6a49f722422f6e3425c52b06245a5cf9bc09908b174f5e27"
-"checksum serde 1.0.23 (registry+https://github.com/rust-lang/crates.io-index)" = "6a7c37d7f192f00041e8a613e936717923a71bc0c9051fc4425a49b104140f05"
-"checksum serde_derive 1.0.23 (registry+https://github.com/rust-lang/crates.io-index)" = "0672de7300b02bac3f3689f8faea813c4a1ea9fe0cb49e80f714231d267518a2"
-"checksum serde_derive_internals 0.17.0 (registry+https://github.com/rust-lang/crates.io-index)" = "32f1926285523b2db55df263d2aa4eb69ddcfa7a7eade6430323637866b513ab"
+"checksum serde 1.0.24 (registry+https://github.com/rust-lang/crates.io-index)" = "1c57ab4ec5fa85d08aaf8ed9245899d9bbdd66768945b21113b84d5f595cb6a1"
+"checksum serde_derive 1.0.24 (registry+https://github.com/rust-lang/crates.io-index)" = "02c92ea07b6e49b959c1481804ebc9bfd92d3c459f1274c9a9546829e42a66ce"
+"checksum serde_derive_internals 0.18.0 (registry+https://github.com/rust-lang/crates.io-index)" = "75c6aac7b99801a16db5b40b7bf0d7e4ba16e76fbf231e32a4677f271cac0603"
 "checksum strsim 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)" = "b4d15c810519a91cf877e7e36e63fe068815c678181439f2f29e2562147c3694"
 "checksum syn 0.11.11 (registry+https://github.com/rust-lang/crates.io-index)" = "d3b891b9015c88c576343b9b3e41c2c11a51c219ef067b264bd9c8aa9b441dad"
 "checksum synom 0.11.3 (registry+https://github.com/rust-lang/crates.io-index)" = "a393066ed9010ebaed60b9eafa373d4b1baac186dd7e008555b0f702b51945b6"
-"checksum thread_local 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)" = "1697c4b57aeeb7a536b647165a2825faddffb1d3bad386d507709bd51a90bb14"
+"checksum thread_local 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)" = "279ef31c19ededf577bfd12dfae728040a21f635b06a24cd670ff510edd38963"
 "checksum unicode-xid 0.0.4 (registry+https://github.com/rust-lang/crates.io-index)" = "8c1f860d7d29cf02cb2f3f359fd35991af3d30bac52c57d265a3c461074cb4dc"
 "checksum unreachable 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "382810877fe448991dfc7f0dd6e3ae5d58088fd0ea5e35189655f84e6814fa56"
 "checksum untrusted 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)" = "f392d7819dbe58833e26872f5f6f0d68b7bbbe90fc3667e98731c4a15ad9a7ae"
diff --git a/sim/mcuboot-sys/csupport/run.c b/sim/mcuboot-sys/csupport/run.c
index d749e49..91d779a 100644
--- a/sim/mcuboot-sys/csupport/run.c
+++ b/sim/mcuboot-sys/csupport/run.c
@@ -1,5 +1,6 @@
 /* Run the boot image. */
 
+#include <assert.h>
 #include <setjmp.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -25,6 +26,8 @@
 int flash_counter;
 
 int jumped = 0;
+uint8_t c_asserts = 0;
+uint8_t c_catch_asserts = 0;
 
 int ecdsa256_sign_(const uint8_t *privkey, const uint8_t *hash,
                    unsigned hash_len, uint8_t *signature)
@@ -249,3 +252,19 @@
 
     return 0;
 }
+
+void sim_assert(int x, const char *assertion, const char *file, unsigned int line, const char *function)
+{
+    if (!(x)) {
+        if (c_catch_asserts) {
+            c_asserts++;
+        } else {
+            BOOT_LOG_ERR("%s:%d: %s: Assertion `%s' failed.", file, line, function, assertion);
+
+            /* NOTE: if the assert below is triggered, the place where it was originally
+             * asserted is printed by the message above...
+             */
+            assert(x);
+        }
+    }
+}
diff --git a/sim/mcuboot-sys/src/c.rs b/sim/mcuboot-sys/src/c.rs
index 9f364cb..3400bc0 100644
--- a/sim/mcuboot-sys/src/c.rs
+++ b/sim/mcuboot-sys/src/c.rs
@@ -13,11 +13,14 @@
 }
 
 /// Invoke the bootloader on this flash device.
-pub fn boot_go(flash: &mut Flash, areadesc: &AreaDesc, counter: Option<&mut i32>, align: u8) -> i32 {
+pub fn boot_go(flash: &mut Flash, areadesc: &AreaDesc, counter: Option<&mut i32>,
+               align: u8, catch_asserts: bool) -> (i32, u8) {
     let _lock = BOOT_LOCK.lock().unwrap();
 
     unsafe {
         api::set_flash(flash);
+        raw::c_catch_asserts = if catch_asserts { 1 } else { 0 };
+        raw::c_asserts = 0u8;
         raw::sim_flash_align = align;
         raw::flash_counter = match counter {
             None => 0,
@@ -25,11 +28,12 @@
         };
     }
     let result = unsafe { raw::invoke_boot_go(&areadesc.get_c() as *const _) as i32 };
+    let asserts = unsafe { raw::c_asserts };
     unsafe {
         counter.map(|c| *c = raw::flash_counter as i32);
         api::clear_flash();
     };
-    result
+    (result, asserts)
 }
 
 pub fn boot_trailer_sz(align: u8) -> u32 {
@@ -65,6 +69,8 @@
         // for information and tracking.
         pub fn invoke_boot_go(areadesc: *const CAreaDesc) -> libc::c_int;
         pub static mut flash_counter: libc::c_int;
+        pub static mut c_asserts: u8;
+        pub static mut c_catch_asserts: u8;
 
         pub static mut sim_flash_align: u8;
         pub fn boot_slots_trailer_sz(min_write_sz: u8) -> u32;
diff --git a/sim/src/lib.rs b/sim/src/lib.rs
index b83e31b..e22984e 100644
--- a/sim/src/lib.rs
+++ b/sim/src/lib.rs
@@ -518,7 +518,8 @@
         info!("Try norevert");
 
         // First do a normal upgrade...
-        if c::boot_go(&mut fl, &self.areadesc, None, self.align) != 0 {
+        let (result, _) = c::boot_go(&mut fl, &self.areadesc, None, self.align, false);
+        if result != 0 {
             warn!("Failed first boot");
             fails += 1;
         }
@@ -550,7 +551,8 @@
             fails += 1;
         }
 
-        if c::boot_go(&mut fl, &self.areadesc, None, self.align) != 0 {
+        let (result, _) = c::boot_go(&mut fl, &self.areadesc, None, self.align, false);
+        if result != 0 {
             warn!("Failed second boot");
             fails += 1;
         }
@@ -589,7 +591,8 @@
         }
 
         // Run the bootloader...
-        if c::boot_go(&mut fl, &self.areadesc, None, self.align) != 0 {
+        let (result, _) = c::boot_go(&mut fl, &self.areadesc, None, self.align, false);
+        if result != 0 {
             warn!("Failed first boot");
             fails += 1;
         }
@@ -636,7 +639,8 @@
         }
 
         // Run the bootloader...
-        if c::boot_go(&mut fl, &self.areadesc, None, self.align) != 0 {
+        let (result, _) = c::boot_go(&mut fl, &self.areadesc, None, self.align, false);
+        if result != 0 {
             warn!("Failed first boot");
             fails += 1;
         }
@@ -658,6 +662,155 @@
 
         fails > 0
     }
+
+    fn trailer_sz(&self) -> usize {
+        c::boot_trailer_sz(self.align) as usize
+    }
+
+    // FIXME: could get status sz from bootloader
+    fn status_sz(&self) -> usize {
+        self.trailer_sz() - (16 + 24)
+    }
+
+    /// This test runs a simple upgrade with no fails in the images, but
+    /// allowing for fails in the status area. This should run to the end
+    /// and warn that write fails were detected...
+    #[cfg(not(feature = "validate-slot0"))]
+    pub fn run_with_status_fails_complete(&self) -> bool { false }
+
+    #[cfg(feature = "validate-slot0")]
+    pub fn run_with_status_fails_complete(&self) -> bool {
+        let mut fl = self.flash.clone();
+        let mut fails = 0;
+
+        info!("Try swap with status fails");
+
+        mark_permanent_upgrade(&mut fl, &self.slot1, self.align);
+
+        let status_off = self.slot1.base_off - self.trailer_sz();
+
+        // Always fail writes to status area...
+        let _ = fl.add_bad_region(status_off, self.status_sz(), 1.0);
+
+        let (result, asserts) = c::boot_go(&mut fl, &self.areadesc, None, self.align, true);
+        if result != 0 {
+            warn!("Failed!");
+            fails += 1;
+        }
+
+        // Failed writes to the marked "bad" region don't assert anymore.
+        // Any detected assert() is happening in another part of the code.
+        if asserts != 0 {
+            warn!("At least one assert() was called");
+            fails += 1;
+        }
+
+        if !verify_trailer(&fl, self.slot0.trailer_off, MAGIC_VALID, IMAGE_OK,
+                           COPY_DONE) {
+            warn!("Mismatched trailer for Slot 0");
+            fails += 1;
+        }
+
+        if !verify_image(&fl, self.slot0.base_off, &self.upgrade) {
+            warn!("Failed image verification");
+            fails += 1;
+        }
+
+        info!("validate slot0 enabled; re-run of boot_go should just work");
+        let (result, _) = c::boot_go(&mut fl, &self.areadesc, None, self.align, false);
+        if result != 0 {
+            warn!("Failed!");
+            fails += 1;
+        }
+
+        if fails > 0 {
+            error!("Error running upgrade with status write fails");
+        }
+
+        fails > 0
+    }
+
+    /// This test runs a simple upgrade with no fails in the images, but
+    /// allowing for fails in the status area. This should run to the end
+    /// and warn that write fails were detected...
+    #[cfg(feature = "validate-slot0")]
+    pub fn run_with_status_fails_with_reset(&self) -> bool {
+        let mut fl = self.flash.clone();
+        let mut fails = 0;
+        let mut count = self.total_count.unwrap() / 2;
+
+        //info!("count={}\n", count);
+
+        info!("Try interrupted swap with status fails");
+
+        mark_permanent_upgrade(&mut fl, &self.slot1, self.align);
+
+        let status_off = self.slot1.base_off - self.trailer_sz();
+
+        // Mark the status area as a bad area
+        let _ = fl.add_bad_region(status_off, self.status_sz(), 0.5);
+
+        // Should not fail, writing to bad regions does not assert
+        let (_, asserts) = c::boot_go(&mut fl, &self.areadesc, Some(&mut count), self.align, true);
+        if asserts != 0 {
+            warn!("At least one assert() was called");
+            fails += 1;
+        }
+
+        fl.reset_bad_regions();
+
+        // Disabling write verification the only assert triggered by
+        // boot_go should be checking for integrity of status bytes.
+        fl.set_verify_writes(false);
+
+        info!("Resuming an interrupted swap operation");
+        let (_, asserts) = c::boot_go(&mut fl, &self.areadesc, None, self.align, true);
+
+        // This might throw no asserts, for large sector devices, where
+        // a single failure writing is indistinguishable from no failure,
+        // or throw a single assert for small sector devices that fail
+        // multiple times...
+        if asserts > 1 {
+            warn!("Expected single assert validating slot0, more detected {}", asserts);
+            fails += 1;
+        }
+
+        if fails > 0 {
+            error!("Error running upgrade with status write fails");
+        }
+
+        fails > 0
+    }
+
+    #[cfg(not(feature = "validate-slot0"))]
+    #[cfg(not(feature = "overwrite-only"))]
+    pub fn run_with_status_fails_with_reset(&self) -> bool {
+        let mut fl = self.flash.clone();
+        let mut fails = 0;
+
+        info!("Try interrupted swap with status fails");
+
+        mark_permanent_upgrade(&mut fl, &self.slot1, self.align);
+
+        let status_off = self.slot1.base_off - self.trailer_sz();
+
+        // Mark the status area as a bad area
+        let _ = fl.add_bad_region(status_off, self.status_sz(), 1.0);
+
+        // This is expected to fail while writing to bad regions...
+        let (_, asserts) = c::boot_go(&mut fl, &self.areadesc, None, self.align, true);
+        if asserts == 0 {
+            warn!("No assert() detected");
+            fails += 1;
+        }
+
+        fails > 0
+    }
+
+    #[cfg(feature = "overwrite-only")]
+    pub fn run_with_status_fails_with_reset(&self) -> bool {
+        false
+    }
 }
 
 /// Test a boot, optionally stopping after 'n' flash options.  Returns a count
@@ -671,19 +824,19 @@
 
     let mut counter = stop.unwrap_or(0);
 
-    let (first_interrupted, count) = match c::boot_go(&mut fl, &images.areadesc, Some(&mut counter), images.align) {
-        -0x13579 => (true, stop.unwrap()),
-        0 => (false, -counter),
-        x => panic!("Unknown return: {}", x),
+    let (first_interrupted, count) = match c::boot_go(&mut fl, &images.areadesc, Some(&mut counter), images.align, false) {
+        (-0x13579, _) => (true, stop.unwrap()),
+        (0, _) => (false, -counter),
+        (x, _) => panic!("Unknown return: {}", x),
     };
 
     counter = 0;
     if first_interrupted {
         // fl.dump();
-        match c::boot_go(&mut fl, &images.areadesc, Some(&mut counter), images.align) {
-            -0x13579 => panic!("Shouldn't stop again"),
-            0 => (),
-            x => panic!("Unknown return: {}", x),
+        match c::boot_go(&mut fl, &images.areadesc, Some(&mut counter), images.align, false) {
+            (-0x13579, _) => panic!("Shouldn't stop again"),
+            (0, _) => (),
+            (x, _) => panic!("Unknown return: {}", x),
         }
     }
 
@@ -697,7 +850,7 @@
     // fl.write_file("image0.bin").unwrap();
     for i in 0 .. count {
         info!("Running boot pass {}", i + 1);
-        assert_eq!(c::boot_go(&mut fl, &areadesc, None, align), 0);
+        assert_eq!(c::boot_go(&mut fl, &areadesc, None, align, false), (0, 0));
     }
     fl
 }
@@ -706,11 +859,10 @@
 fn try_revert_with_fail_at(flash: &SimFlash, images: &Images,
                            stop: i32) -> bool {
     let mut fl = flash.clone();
-    let mut x: i32;
     let mut fails = 0;
 
     let mut counter = stop;
-    x = c::boot_go(&mut fl, &images.areadesc, Some(&mut counter), images.align);
+    let (x, _) = c::boot_go(&mut fl, &images.areadesc, Some(&mut counter), images.align, false);
     if x != -0x13579 {
         warn!("Should have stopped at interruption point");
         fails += 1;
@@ -721,7 +873,7 @@
         fails += 1;
     }
 
-    x = c::boot_go(&mut fl, &images.areadesc, None, images.align);
+    let (x, _) = c::boot_go(&mut fl, &images.areadesc, None, images.align, false);
     if x != 0 {
         warn!("Should have finished upgrade");
         fails += 1;
@@ -747,7 +899,7 @@
     }
 
     // Do Revert
-    x = c::boot_go(&mut fl, &images.areadesc, None, images.align);
+    let (x, _) = c::boot_go(&mut fl, &images.areadesc, None, images.align, false);
     if x != 0 {
         warn!("Should have finished a revert");
         fails += 1;
@@ -788,18 +940,18 @@
         let ops = Range::new(1, remaining_ops / 2);
         let reset_counter = ops.ind_sample(&mut rng);
         let mut counter = reset_counter;
-        match c::boot_go(&mut fl, &images.areadesc, Some(&mut counter), images.align) {
-            0 | -0x13579 => (),
-            x => panic!("Unknown return: {}", x),
+        match c::boot_go(&mut fl, &images.areadesc, Some(&mut counter), images.align, false) {
+            (0, _) | (-0x13579, _) => (),
+            (x, _) => panic!("Unknown return: {}", x),
         }
         remaining_ops -= reset_counter;
         resets[i] = reset_counter;
     }
 
-    match c::boot_go(&mut fl, &images.areadesc, None, images.align) {
-        -0x13579 => panic!("Should not be have been interrupted!"),
-        0 => (),
-        x => panic!("Unknown return: {}", x),
+    match c::boot_go(&mut fl, &images.areadesc, None, images.align, false) {
+        (-0x13579, _) => panic!("Should not be have been interrupted!"),
+        (0, _) => (),
+        (x, _) => panic!("Unknown return: {}", x),
     }
 
     (fl, resets)