diff --git a/src/check.c b/src/check.c
index f74b384..89df345 100644
--- a/src/check.c
+++ b/src/check.c
@@ -362,25 +362,24 @@ void _mark_point(const char *file, int line)
     send_loc_info(file, line);
 }
 
-void _ck_assert_failed(const char *file, int line, const char *expr, ...)
+void _ck_assert_failed(const char *file, int line, const char *expr,
+                       const char *msg, ...)
 {
-    const char *msg;
-    va_list ap;
     char buf[BUFSIZ];
     const char *to_send;
 
     send_loc_info(file, line);
 
-    va_start(ap, expr);
-    msg = (const char *)va_arg(ap, char *);
-
     /*
      * If a message was passed, format it with vsnprintf.
      * Otherwise, print the expression as is.
      */
     if(msg != NULL)
     {
+        va_list ap;
+        va_start(ap, msg);
         vsnprintf(buf, BUFSIZ, msg, ap);
+        va_end(ap);
         to_send = buf;
     }
     else
@@ -388,7 +387,6 @@ void _ck_assert_failed(const char *file, int line, const char *expr, ...)
         to_send = expr;
     }
 
-    va_end(ap);
     send_failure_info(to_send);
     if(cur_fork_status() == CK_FORK)
     {
diff --git a/src/check.h.in b/src/check.h.in
index fdbc8b0..9baddc9 100644
--- a/src/check.h.in
+++ b/src/check.h.in
@@ -480,7 +480,7 @@ static void __testname ## _fn (int _i CK_ATTRIBUTE_UNUSED)
  */
 #define fail_if(expr, ...)\
   (expr) ? \
-     _ck_assert_failed(__FILE__, __LINE__, "Failure '"#expr"' occurred" , ## __VA_ARGS__, NULL) \
+     _ck_assert_failed(__FILE__, __LINE__, "Failure '"#expr"' occurred" , ## __VA_ARGS__) \
      : _mark_point(__FILE__, __LINE__)
 
 /*
@@ -500,11 +500,12 @@ static void __testname ## _fn (int _i CK_ATTRIBUTE_UNUSED)
  */
 #if @HAVE_FORK@
 CK_DLL_EXP void CK_EXPORT _ck_assert_failed(const char *file, int line,
-                                            const char *expr,
-                                            ...) CK_ATTRIBUTE_NORETURN CK_ATTRIBUTE_FORMAT(gnu_printf, 3, 4);
+                                            const char *expr, const char *msg,
+                                            ...) CK_ATTRIBUTE_NORETURN CK_ATTRIBUTE_FORMAT(gnu_printf, 4, 5);
 #else
 CK_DLL_EXP void CK_EXPORT _ck_assert_failed(const char *file, int line,
-                                            const char *expr, ...) CK_ATTRIBUTE_FORMAT(gnu_printf, 3, 4);
+                                            const char *expr, const char *msg,
+                                            ...) CK_ATTRIBUTE_FORMAT(gnu_printf, 4, 5);
 #endif
 
 /**
@@ -534,7 +535,7 @@ CK_DLL_EXP void CK_EXPORT _ck_assert_failed(const char *file, int line,
 #define ck_assert_msg(expr, ...) \
   (expr) ? \
      _mark_point(__FILE__, __LINE__) : \
-     _ck_assert_failed(__FILE__, __LINE__, "Assertion '"#expr"' failed" , ## __VA_ARGS__, NULL)
+     _ck_assert_failed(__FILE__, __LINE__, "Assertion '"#expr"' failed" , ## __VA_ARGS__)
 
 /**
  * Unconditionally fail the test
@@ -553,7 +554,7 @@ CK_DLL_EXP void CK_EXPORT _ck_assert_failed(const char *file, int line,
  *
  * @since 0.9.6
  */
-#define ck_abort_msg(...) _ck_assert_failed(__FILE__, __LINE__, "Failed" , ## __VA_ARGS__, NULL)
+#define ck_abort_msg(...) _ck_assert_failed(__FILE__, __LINE__, "Failed" , ## __VA_ARGS__)
 
 /* Signed and unsigned integer comparison macros with improved output compared to ck_assert(). */
 /* OP may be any comparison operator. */