diff --git a/rebase.go b/rebase.go
index 0fd05dd..881c836 100644
--- a/rebase.go
+++ b/rebase.go
@@ -3,6 +3,7 @@ package git
 /*
 #include <git2.h>
 
+extern void _go_git_buf_fill_null(git_buf *buf);
 extern void _go_git_populate_commit_sign_cb(git_rebase_options *opts);
 */
 import "C"
@@ -102,6 +103,8 @@ func commitSignCallback(_signature *C.git_buf, _signature_field *C.git_buf, _com
 			return errors.New("could not grow buffer")
 		}
 
+		C._go_git_buf_fill_null(buf)
+
 		if int(C.git_buf_set(buf, cstr, clen)) != 0 {
 			return errors.New("could not set buffer")
 		}
diff --git a/wrapper.c b/wrapper.c
index 90bcf6b..ddb4126 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -6,6 +6,11 @@
 
 typedef int (*gogit_submodule_cbk)(git_submodule *sm, const char *name, void *payload);
 
+void _go_git_buf_fill_null(git_buf *buf)
+{
+  memset(buf->ptr, '\0', buf->asize*sizeof(char));
+}
+
 void _go_git_populate_commit_sign_cb(git_rebase_options *opts)
 {
   opts->signing_cb = (git_commit_signing_cb)commitSignCallback;