diff --git a/PyMca/Object3D/Object3DQhull/src/io.c b/PyMca/Object3D/Object3DQhull/src/io.c
index c219100..38d301d 100755
--- a/PyMca/Object3D/Object3DQhull/src/io.c
+++ b/PyMca/Object3D/Object3DQhull/src/io.c
@@ -2166,7 +2166,7 @@ void qh_printfacet3math (FILE *fp, facetT *facet, int format, int notfirst) {
     qh_memfree (point, qh normal_size);
   qh_settempfree(&points);
   qh_settempfree(&vertices);
-  fprintf(fp, endfmt);
+  fprintf(fp, "%s", endfmt);
 } /* printfacet3math */