diff --git a/artiq/runtime/session.c b/artiq/runtime/session.c
index 5c4333480..fb6e4dcaf 100644
--- a/artiq/runtime/session.c
+++ b/artiq/runtime/session.c
@@ -1027,7 +1027,6 @@ static int process_kmsg(struct msg_base *umsg)
             struct cache_row *row = NULL;
             for(struct cache_row *iter = cache; iter; iter = iter->next) {
                 if(!strcmp(iter->key, request->key)) {
-                    free(iter->elements);
                     row = iter;
                     break;
                 }
@@ -1042,11 +1041,14 @@ static int process_kmsg(struct msg_base *umsg)
             }
 
             if(!row->borrowed) {
-                if(request->length != 0) {
-                    row->length = request->length;
+                row->length = request->length;
+                if(row->length != 0) {
                     row->elements = calloc(row->length, sizeof(int32_t));
                     memcpy(row->elements, request->elements,
                            sizeof(int32_t) * row->length);
+                } else {
+                    free(row->elements);
+                    row->elements = NULL;
                 }
 
                 reply.succeeded = 1;