diff --git a/src/mustach.c b/src/mustach.c
index 9868cff..e2da8b2 100644
--- a/src/mustach.c
+++ b/src/mustach.c
@@ -38,7 +38,7 @@ static int getpartial(struct mustach_itf *itf, void *closure, const char *name,
 
 	*result = NULL;
 	file = open_memstream(result, &size);
-	if (file == NULL)
+	if (itf->put == NULL || file == NULL)
 		rc = MUSTACH_ERROR_SYSTEM;
 	else {
 		rc = itf->put(closure, name, 0, file);
@@ -192,6 +192,8 @@ static int process(const char *template, struct mustach_itf *itf, void *closure,
 		default:
 			/* replacement */
 			if (emit) {
+				if (itf->put == NULL)
+					return MUSTACH_ERROR_SYSTEM;
 				rc = itf->put(closure, name, c != '&', file);
 				if (rc < 0)
 					return rc;