diff --git a/src/hyperloglog.c b/src/hyperloglog.c
index bb07aa3800bb663bcfe40d2be043d374b761d5ba..3cb31f2965f2fe7175497aae946bcd16a85fb7d2 100644
--- a/src/hyperloglog.c
+++ b/src/hyperloglog.c
@@ -1427,6 +1427,21 @@ void pfdebugCommand(redisClient *c) {
         if (c->argc != 3) goto arityerr;
 
         addReplyStatus(c,encodingstr[hdr->encoding]);
+    }
+    /* PFDEBUG TODENSE <key> */
+    else if (!strcasecmp(cmd,"todense")) {
+        int conv = 0;
+        if (c->argc != 3) goto arityerr;
+
+        if (hdr->encoding == HLL_SPARSE) {
+            if (hllSparseToDense(o) == REDIS_ERR) {
+                addReplyError(c,invalid_hll_err);
+                return;
+            }
+            conv = 1;
+            server.dirty++; /* Force propagation on encoding change. */
+        }
+        addReply(c,conv ? shared.cone : shared.czero);
     } else {
         addReplyErrorFormat(c,"Unknown PFDEBUG subcommand '%s'", cmd);
     }