diff --git a/lib/oid_registry.c b/lib/oid_registry.c
index 318f382..41b9e50 100644
--- a/lib/oid_registry.c
+++ b/lib/oid_registry.c
@@ -142,9 +142,9 @@
 		}
 		ret += count = snprintf(buffer, bufsize, ".%lu", num);
 		buffer += count;
-		bufsize -= count;
-		if (bufsize == 0)
+		if (bufsize <= count)
 			return -ENOBUFS;
+		bufsize -= count;
 	}
 
 	return ret;