thodg/libgit2

diff --git a/src/common.h b/src/common.h
index 51fb918..f12cc98 100644
--- a/src/common.h
+++ b/src/common.h
@@ -103,7 +103,8 @@
 /**
  * Set the error message for this thread, formatting as needed.
  */
-void giterr_set(int error_class, const char *string, ...);
+
+void giterr_set(int error_class, const char *string, ...) GIT_FORMAT_PRINTF(2, 3);
 
 /**
  * Set the error message for a regex failure, using the internal regex