diff --git a/sim/mcuboot-sys/build.rs b/sim/mcuboot-sys/build.rs
index 516741b..81e21d1 100644
--- a/sim/mcuboot-sys/build.rs
+++ b/sim/mcuboot-sys/build.rs
@@ -17,6 +17,7 @@
     let mut conf = gcc::Build::new();
     conf.define("__BOOTSIM__", None);
     conf.define("MCUBOOT_USE_FLASH_AREA_GET_SECTORS", None);
+    conf.define("MCUBOOT_HAVE_ASSERT_H", None);
     conf.define("MCUBOOT_MAX_IMG_SECTORS", Some("128"));
 
     if validate_slot0 {
diff --git a/sim/mcuboot-sys/csupport/bootsim.h b/sim/mcuboot-sys/csupport/bootsim.h
index f3fc5e4..3245ec3 100644
--- a/sim/mcuboot-sys/csupport/bootsim.h
+++ b/sim/mcuboot-sys/csupport/bootsim.h
@@ -1,7 +1,6 @@
 #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__)
+#include "mcuboot_config/mcuboot_assert.h"
 
 #endif
diff --git a/sim/mcuboot-sys/csupport/mcuboot_config/mcuboot_assert.h b/sim/mcuboot-sys/csupport/mcuboot_config/mcuboot_assert.h
new file mode 100644
index 0000000..3f1ce90
--- /dev/null
+++ b/sim/mcuboot-sys/csupport/mcuboot_config/mcuboot_assert.h
@@ -0,0 +1,7 @@
+#ifndef __MCUBOOT_ASSERT_H__
+#define __MCUBOOT_ASSERT_H__
+
+void sim_assert(int, const char *test, const char *, unsigned int, const char *);
+#define ASSERT(x) sim_assert((x), #x, __FILE__, __LINE__, __func__)
+
+#endif  /* __MCUBOOT_ASSERT_H__ */