diff --git a/src/openttd.cpp b/src/openttd.cpp
index 58f011b082..cc382bdbf0 100644
--- a/src/openttd.cpp
+++ b/src/openttd.cpp
@@ -123,6 +123,25 @@ void CDECL error(const char *s, ...)
 	abort();
 }
 
+void CDECL assert_msg_error(int line, const char *file, const char *expr, const char *str, ...)
+{
+	va_list va;
+	char buf[2048];
+
+	char *b = buf;
+	b += seprintf(b, lastof(buf), "Assertion failed at line %i of %s: %s\n\t", line, file, expr);
+
+	va_start(va, str);
+	vseprintf(b, lastof(buf), str, va);
+	va_end(va);
+
+	ShowOSErrorBox(buf, true);
+
+	/* Set the error message for the crash log and then invoke it. */
+	CrashLog::SetErrorMessage(buf);
+	abort();
+}
+
 /**
  * Shows some information on the console/a popup box depending on the OS.
  * @param str the text to show.
diff --git a/src/stdafx.h b/src/stdafx.h
index 4ca0a12c30..cf9fe92f99 100644
--- a/src/stdafx.h
+++ b/src/stdafx.h
@@ -433,6 +433,7 @@ assert_compile(SIZE_MAX >= UINT32_MAX);
 
 void NORETURN CDECL usererror(const char *str, ...) WARN_FORMAT(1, 2);
 void NORETURN CDECL error(const char *str, ...) WARN_FORMAT(1, 2);
+void NORETURN CDECL assert_msg_error(int line, const char *file, const char *expr, const char *str, ...) WARN_FORMAT(4, 5);
 #define NOT_REACHED() error("NOT_REACHED triggered at line %i of %s", __LINE__, __FILE__)
 
 /* For non-debug builds with assertions enabled use the special assertion handler:
@@ -447,6 +448,9 @@ void NORETURN CDECL error(const char *str, ...) WARN_FORMAT(1, 2);
 /* Asserts are enabled if NDEBUG isn't defined, or if we are using MSVC and WITH_ASSERT is defined. */
 #if !defined(NDEBUG) || (defined(_MSC_VER) && defined(WITH_ASSERT))
 	#define OTTD_ASSERT
+	#define assert_msg(expression, ...) if (!(expression)) assert_msg_error(__LINE__, __FILE__, #expression, __VA_ARGS__);
+#else
+	#define assert_msg(expression, ...)
 #endif
 
 #if defined(MORPHOS) || defined(__NDS__) || defined(__DJGPP__)