diff --git a/modAionImpl/src/org/aion/zero/impl/types/AionBlock.java b/modAionImpl/src/org/aion/zero/impl/types/AionBlock.java
index 6aed5896bc..0ef8dcb95f 100644
--- a/modAionImpl/src/org/aion/zero/impl/types/AionBlock.java
+++ b/modAionImpl/src/org/aion/zero/impl/types/AionBlock.java
@@ -456,4 +456,8 @@ public void updateHeaderDifficulty(byte[] diff) {
                 .withDifficulty(diff)
                 .build();
     }
+
+    public boolean notSealed() {
+        return Arrays.equals(header.getSolution(), new byte[A0BlockHeader.SOLUTIONSIZE]) && Arrays.equals(header.getNonce(), ByteUtil.EMPTY_WORD);
+    }
 }
diff --git a/modApiServer/src/org/aion/api/server/rpc/ApiWeb3Aion.java b/modApiServer/src/org/aion/api/server/rpc/ApiWeb3Aion.java
index 25e24798c2..9d6e85f62d 100644
--- a/modApiServer/src/org/aion/api/server/rpc/ApiWeb3Aion.java
+++ b/modApiServer/src/org/aion/api/server/rpc/ApiWeb3Aion.java
@@ -2612,7 +2612,7 @@ public RpcMsg stratum_submitblock(Object _params) {
                 && !JSONObject.NULL.equals(hdrHash)) {
             // Grab copy of best block
             AionBlock bestBlock = ac.getBlockchain().getCachingMiningBlockTemplate(hexStringToBytes((String) hdrHash));
-            if (bestBlock != null) {
+            if (bestBlock != null && bestBlock.notSealed()) {
                 try {
                     bestBlock.seal(hexStringToBytes(nce + ""), hexStringToBytes(soln + ""));
                 } catch (Exception e) {