diff --git a/keygen/primecandidate.c b/keygen/primecandidate.c
index 02c0259d..fca2b297 100644
--- a/keygen/primecandidate.c
+++ b/keygen/primecandidate.c
@@ -396,6 +396,8 @@ mp_int *pcs_generate(PrimeCandidateSource *s)
 
         if (!ok) {
             mp_free(x);
+            if (s->one_shot)
+                return NULL;
             continue; /* try a new x */
         }