diff --git a/src/core/vsprintf.c b/src/core/vsprintf.c
index cb3bec5d..9d3a97c2 100644
--- a/src/core/vsprintf.c
+++ b/src/core/vsprintf.c
@@ -257,11 +257,13 @@ size_t vcprintf ( struct printf_context *ctx, const char *fmt, va_list args ) {
 		} else if ( *fmt == 's' ) {
 			if ( length < &type_sizes[LONG_LEN] ) {
 				ptr = va_arg ( args, char * );
+				if ( ! ptr )
+					ptr = "<NULL>";
 			} else {
 				wptr = va_arg ( args, wchar_t * );
+				if ( ! wptr )
+					ptr = "<NULL>";
 			}
-			if ( ( ptr == NULL ) && ( wptr == NULL ) )
-				ptr = "<NULL>";
 		} else if ( *fmt == 'p' ) {
 			intptr_t ptrval;
 
diff --git a/src/tests/vsprintf_test.c b/src/tests/vsprintf_test.c
index ad732a0d..f388b3de 100644
--- a/src/tests/vsprintf_test.c
+++ b/src/tests/vsprintf_test.c
@@ -108,6 +108,10 @@ static void vsprintf_test_exec ( void ) {
 	snprintf_ok ( 64, "PCI 00:1f.3", "PCI %02x:%02x.%x", 0x00, 0x1f, 0x03 );
 	snprintf_ok ( 64, "Region [1000000,3f000000)", "Region [%llx,%llx)",
 		      0x1000000ULL, 0x3f000000ULL );
+
+	/* Null string (used for debug messages) */
+	snprintf_ok ( 16, "<NULL>", "%s", ( ( char * ) NULL ) );
+	snprintf_ok ( 16, "<NULL>", "%ls", ( ( wchar_t * ) NULL ) );
 }
 
 /** vsprintf() self-test */