diff --git a/boot/bootutil/src/bootutil_misc.c b/boot/bootutil/src/bootutil_misc.c
index 7229a5d..0ec8605 100644
--- a/boot/bootutil/src/bootutil_misc.c
+++ b/boot/bootutil/src/bootutil_misc.c
@@ -34,12 +34,6 @@
 #define BOOT_LOG_LEVEL BOOT_LOG_LEVEL_INFO
 #include "bootutil/bootutil_log.h"
 
-#ifdef __BOOTSIM__
-#undef assert
-void sim_assert(int, const char *test, const char *, unsigned int, const char *);
-#define assert(x) sim_assert((x), #x, __FILE__, __LINE__, __func__)
-#endif
-
 int boot_current_slot;
 
 const uint32_t boot_img_magic[] = {
diff --git a/boot/bootutil/src/bootutil_priv.h b/boot/bootutil/src/bootutil_priv.h
index 08e8c83..1fd0403 100644
--- a/boot/bootutil/src/bootutil_priv.h
+++ b/boot/bootutil/src/bootutil_priv.h
@@ -28,6 +28,12 @@
 extern "C" {
 #endif
 
+#ifdef __BOOTSIM__
+#include "bootsim.h"
+#else
+#define ASSERT assert
+#endif
+
 struct flash_area;
 
 #define BOOT_EFLASH     1
diff --git a/boot/bootutil/src/loader.c b/boot/bootutil/src/loader.c
index fbbc805..75494f6 100644
--- a/boot/bootutil/src/loader.c
+++ b/boot/bootutil/src/loader.c
@@ -41,12 +41,6 @@
 #include "mcuboot_config/mcuboot_config.h"
 #endif
 
-#ifdef __BOOTSIM__
-#undef assert
-void sim_assert(int, const char *test, const char *, unsigned int, const char *);
-#define assert(x) sim_assert((x), #x, __FILE__, __LINE__, __func__)
-#endif
-
 static struct boot_loader_state boot_data;
 
 #ifdef MCUBOOT_VALIDATE_SLOT0
@@ -58,7 +52,7 @@
         }                                    \
     } while (0)
 #else
-#define BOOT_STATUS_ASSERT(x) assert(x)
+#define BOOT_STATUS_ASSERT(x) ASSERT(x)
 #endif
 
 struct boot_status_table {
@@ -1429,7 +1423,7 @@
 
 #ifdef MCUBOOT_VALIDATE_SLOT0
     rc = boot_validate_slot(0);
-    assert(rc == 0);
+    ASSERT(rc == 0);
     if (rc != 0) {
         rc = BOOT_EBADIMAGE;
         goto out;
diff --git a/sim/mcuboot-sys/build.rs b/sim/mcuboot-sys/build.rs
index 5f5eeac..ebff3c5 100644
--- a/sim/mcuboot-sys/build.rs
+++ b/sim/mcuboot-sys/build.rs
@@ -81,6 +81,7 @@
     conf.file("csupport/run.c");
     conf.include("../../boot/bootutil/include");
     conf.include("../../boot/zephyr/include");
+    conf.include("csupport");
     conf.debug(true);
     conf.flag("-Wall");
     conf.flag("-Werror");
diff --git a/sim/mcuboot-sys/csupport/bootsim.h b/sim/mcuboot-sys/csupport/bootsim.h
new file mode 100644
index 0000000..f3fc5e4
--- /dev/null
+++ b/sim/mcuboot-sys/csupport/bootsim.h
@@ -0,0 +1,7 @@
+#ifndef H_BOOTSIM_
+#define H_BOOTSIM_
+
+void sim_assert(int, const char *test, const char *, unsigned int, const char *);
+#define ASSERT(x) sim_assert((x), #x, __FILE__, __LINE__, __func__)
+
+#endif
diff --git a/sim/mcuboot-sys/csupport/run.c b/sim/mcuboot-sys/csupport/run.c
index 91d779a..9b5e36e 100644
--- a/sim/mcuboot-sys/csupport/run.c
+++ b/sim/mcuboot-sys/csupport/run.c
@@ -10,6 +10,7 @@
 #include "flash_map/flash_map.h"
 
 #include "../../../boot/bootutil/src/bootutil_priv.h"
+#include "bootsim.h"
 
 #ifdef MCUBOOT_SIGN_EC256
 #include "../../../ext/tinycrypt/lib/include/tinycrypt/ecc_dsa.h"