diff --git a/src/crt.cpp b/src/crt.cpp
index ab6af2b..a13400a 100644
--- a/src/crt.cpp
+++ b/src/crt.cpp
@@ -166,7 +166,11 @@ namespace bx
 				size += writeRep(_writer, _param.fill, padding, _err);
 			}
 
-			if (_param.upper)
+			if (NULL == _str)
+			{
+				size += write(_writer, "(null)", 6, _err);
+			}
+			else if (_param.upper)
 			{
 				for (int32_t ii = 0; ii < len; ++ii)
 				{
diff --git a/src/string.cpp b/src/string.cpp
index 3e927f9..b003494 100644
--- a/src/string.cpp
+++ b/src/string.cpp
@@ -107,8 +107,13 @@ namespace bx
 
 	size_t strnlen(const char* _str, size_t _max)
 	{
-		const char* ptr;
-		for (ptr = _str; 0 < _max && *ptr != '\0'; ++ptr, --_max) {};
+		if (NULL == _str)
+		{
+			return 0;
+		}
+
+		const char* ptr = _str;
+		for (; 0 < _max && *ptr != '\0'; ++ptr, --_max) {};
 		return ptr - _str;
 	}
 
diff --git a/tests/vsnprintf_test.cpp b/tests/vsnprintf_test.cpp
index d85fae0..eca14bb 100644
--- a/tests/vsnprintf_test.cpp
+++ b/tests/vsnprintf_test.cpp
@@ -38,7 +38,7 @@ static bool test(const char* _expected, const char* _format, ...)
 
 	if (!result)
 	{
-		printf("result (%d) %s, expected (%d) %s\n", len, temp, max-1, _expected);
+		printf("result (%d) '%s', expected (%d) '%s'\n", len, temp, max-1, _expected);
 	}
 
 	return result;
@@ -89,6 +89,11 @@ TEST_CASE("vsnprintf p", "")
 	REQUIRE(test("0xbadc0de           ", "%-20p", (void*)0xbadc0de) );
 }
 
+TEST_CASE("vsnprintf s", "")
+{
+	REQUIRE(test("(null)", "%s", NULL) );
+}
+
 TEST_CASE("vsnprintf", "")
 {
 	REQUIRE(test("x", "%c", 'x') );