diff --git a/src/sds.h b/src/sds.h
index 1bdb60dec..adcc12c0a 100644
--- a/src/sds.h
+++ b/src/sds.h
@@ -34,7 +34,7 @@
 #define __SDS_H
 
 #define SDS_MAX_PREALLOC (1024*1024)
-const char *SDS_NOINIT;
+extern const char *SDS_NOINIT;
 
 #include <sys/types.h>
 #include <stdarg.h>