diff --git a/src/udunits.cpp b/src/udunits.cpp
index eb294e1..2d0cacd 100644
--- a/src/udunits.cpp
+++ b/src/udunits.cpp
@@ -20,7 +20,7 @@ extern "C" {
   void r_error_fn(const char* fmt, va_list args) {
     char buf[256];
     vsnprintf(buf, (size_t) 256, fmt, args);
-    Rf_error(buf);
+    Rf_error("%s", buf);
   }
 }