diff --git a/src/binary_c_string_macros.h b/src/binary_c_string_macros.h
index 1998db5ea68ec7ded6b9106db5068f67ffb17a07..3ac061a61ac21bd31bba49c1988f5531fe498374 100644
--- a/src/binary_c_string_macros.h
+++ b/src/binary_c_string_macros.h
@@ -94,7 +94,7 @@
         (                                                               \
             (S)[0] == '\0' ||                                           \
             (                                                           \
-                ((S)[0] == '0' && (S)[0] == '\0')                       \
+                ((S)[0] == '0' && (S)[1] == '\0')                       \
                 ||                                                      \
                 (                                                       \
                     ((S)[0] == 'F' ||                                   \