diff --git a/src/obitypes.h b/src/obitypes.h
index b64dd46..a5399ea 100644
--- a/src/obitypes.h
+++ b/src/obitypes.h
@@ -22,10 +22,10 @@
 #define OBIIdx_NA (INT64_MIN)		/**< NA value for indices */
 #define OBIFloat_NA (float_NA())	/**< NA value for the type OBI_FLOAT */
 #define OBIChar_NA (0)				/**< NA value for the type OBI_CHAR */ // TODO not sure about this one as it can be impossible to distinguish from uninitialized values
-#define OBISeq_NA ("\0")			/**< NA value for the type OBI_SEQ */  // TODO discuss
-#define OBIStr_NA ("\0")			/**< NA value for the type OBI_STR */  // TODO discuss
-#define OBIQual_char_NA ("\0")		/**< NA value for the type OBI_QUAL if the quality is in character string format */  // TODO test and discuss
-#define OBIQual_int_NA (NULL)		/**< NA value for the type OBI_QUAL if the quality is in integer format */  // TODO test and discuss
+#define OBISeq_NA (NULL)			/**< NA value for the type OBI_SEQ */  // TODO discuss
+#define OBIStr_NA (NULL)			/**< NA value for the type OBI_STR */  // TODO discuss
+#define OBIQual_char_NA (NULL)		/**< NA value for the type OBI_QUAL if the quality is in character string format */
+#define OBIQual_int_NA (NULL)		/**< NA value for the type OBI_QUAL if the quality is in integer format */
 
 
 /**