diff --git a/src/Dropper.sol b/src/Dropper.sol
index efb0e95..b590ac0 100644
--- a/src/Dropper.sol
+++ b/src/Dropper.sol
@@ -69,6 +69,7 @@ contract Dropper {
     error InsufficientTokensRemaining();
     error InvalidMerkleProof();
     error ArityMismatch();
+    error DropIdInvalid();
 
     mapping(uint256 => DropData) public drops;
     mapping(uint256 => mapping(address => bool)) private _claimed;
@@ -185,6 +186,7 @@ contract Dropper {
      * @param dropId The drop ID of the drop to refund
      */
     function refundToRecipient(uint256 dropId) external {
+        if (dropId > numDrops || dropId == 0) revert DropIdInvalid();
         DropData storage drop = drops[dropId];
         if (drop.expirationTimestamp > block.timestamp) revert DropStillLive();
         if (drop.totalTokens == drop.claimedTokens) revert AllTokensClaimed();
@@ -206,6 +208,7 @@ contract Dropper {
      * @param merkleProof The merkle inclusion proof
      */
     function claim(uint256 dropId, uint256 amount, bytes32[] calldata merkleProof) public {
+        if (dropId > numDrops || dropId == 0) revert DropIdInvalid();
         DropData storage drop = drops[dropId];
 
         if (drop.expirationTimestamp <= block.timestamp || block.timestamp < drop.startTimestamp) revert DropNotLive();
diff --git a/test/Dropper.t.sol b/test/Dropper.t.sol
index d9ae05b..d78b2c6 100644
--- a/test/Dropper.t.sol
+++ b/test/Dropper.t.sol
@@ -342,6 +342,19 @@ contract DropperTest is PRBTest, StdCheats {
         assertEq(token.balanceOf(address(this)), tokensToRefund);
     }
 
+    function test_refundToRecipient_reverts_dropIdInvalid() public {
+        (uint256 dropId,) =
+            testCreateDrop([address(1), address(2), address(3), address(4)], [uint40(100), 1000, 1000, 1000]);
+
+        vm.warp(block.timestamp + 3601);
+
+        vm.expectRevert(Dropper.DropIdInvalid.selector);
+        dropper.refundToRecipient(dropId + 1);
+
+        vm.expectRevert(Dropper.DropIdInvalid.selector);
+        dropper.refundToRecipient(0);
+    }
+
     function test_createDrop_fail_endBeforeStart() external {
         vm.expectRevert(Dropper.EndBeforeStart.selector);
         dropper.createDrop(