diff --git a/source/lib/util_str.c b/source/lib/util_str.c
index 285b0cc02eb..6005a3e49a0 100644
--- a/source/lib/util_str.c
+++ b/source/lib/util_str.c
@@ -1091,6 +1091,21 @@ size_t strlen_m(const char *s)
 	return count + strlen_w(tmpbuf);
 }
 
+/**
+   Work out the number of multibyte chars in a string, including the NULL
+   terminator.
+**/
+size_t strlen_m_term(const char *s)
+{
+	size_t count = 0;
+
+	if (!s) {
+		return 0;
+	}
+
+	return strlen_m(s) + 1;
+}
+
 /**
  Convert a string to upper case.
 **/
diff --git a/source/librpc/idl/winreg.idl b/source/librpc/idl/winreg.idl
index c7dc3942dfc..263946bdda9 100644
--- a/source/librpc/idl/winreg.idl
+++ b/source/librpc/idl/winreg.idl
@@ -10,8 +10,8 @@
 ] interface winreg
 {
 	typedef struct {
-		[value(2*(strlen_m(r->name)+1))] uint16 name_len;
-		[value(r->name_len)]             uint16 name_size;
+		[value(strlen_m_term(r->name)*2)] uint16 name_len;
+		[value(r->name_len)]              uint16 name_size;
 		unistr *name;
 	} winreg_String;