diff --git a/boot/bootutil/src/bootutil_misc.c b/boot/bootutil/src/bootutil_misc.c
index 0ec8605..7229a5d 100644
--- a/boot/bootutil/src/bootutil_misc.c
+++ b/boot/bootutil/src/bootutil_misc.c
@@ -34,6 +34,12 @@
 #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/loader.c b/boot/bootutil/src/loader.c
index 99ffcd3..fb59401 100644
--- a/boot/bootutil/src/loader.c
+++ b/boot/bootutil/src/loader.c
@@ -41,6 +41,12 @@
 #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;
 
 struct boot_status_table {