diff --git a/src/config.h.W32 b/src/config.h.W32
index 5488021f..369e897d 100644
--- a/src/config.h.W32
+++ b/src/config.h.W32
@@ -343,11 +343,15 @@ this program.  If not, see <https://www.gnu.org/licenses/>.  */
 /* #undef HAVE_STRSIGNAL */
 
 /* Define to 1 if you have the `strtoll' function. */
-#ifdef __TINYC__
-#define strtoll _strtoi64
-#define strtoull _strtoui64
-#endif
 #define HAVE_STRTOLL 1
+#ifdef __TINYC__
+# ifndef strtoll
+#  define strtoll _strtoi64
+# endif
+# ifndef strtoull
+#  define strtoull _strtoui64
+# endif
+#endif
 
 /* Define to 1 if `d_type' is a member of `struct dirent'. */
 /* SV 57152: MinGW64 version of dirent doesn't support d_type. */