diff --git a/libr/include/r_util/r_str.h b/libr/include/r_util/r_str.h
index 03aa1c65101e93..ae02101ab245e6 100644
--- a/libr/include/r_util/r_str.h
+++ b/libr/include/r_util/r_str.h
@@ -66,7 +66,7 @@ typedef struct r_charset_t {
 #define R_STR_ISEMPTY(x) (!(x) || !*(x))
 #define R_STR_ISNOTEMPTY(x) ((x) && *(x))
 #define R_STR_DUP(x) (((x) != NULL) ? strdup ((x)) : NULL)
-#define R_STR_NDUP(ptr, len) ((!ptr || len < 0) ? NULL : strndup (ptr, len))
+#define R_STR_NDUP(ptr, len) ((((ptr) == NULL) || len < 0) ? NULL : strndup (ptr, len))
 #define r_str_array(x,y) ((y >= 0 && y < (sizeof (x) / sizeof (*(x))))?(x)[(y)]: "")
 R_API RCharset *r_charset_new(void);
 R_API void r_charset_free(RCharset *charset);