diff --git a/src/Vm.sol b/src/Vm.sol
index f919e6db..b6dff88c 100644
--- a/src/Vm.sol
+++ b/src/Vm.sol
@@ -10,6 +10,14 @@ pragma experimental ABIEncoderV2;
 // 3. Otherwise you're `pure`.
 
 interface VmSafe {
+    enum CallerMode {
+        None,
+        Broadcast,
+        RecurrentBroadcast,
+        Prank,
+        RecurrentPrank
+    }
+
     struct Log {
         bytes32[] topics;
         bytes data;
@@ -380,6 +388,8 @@ interface Vm is VmSafe {
     function startPrank(address msgSender, address txOrigin) external;
     // Resets subsequent calls' msg.sender to be `address(this)`
     function stopPrank() external;
+    // Reads the current `msg.sender` and `tx.origin` from state and reports if there is any active caller modification
+    function readCallers() external returns (CallerMode callerMode, address msgSender, address txOrigin);
     // Sets an address' balance
     function deal(address account, uint256 newBalance) external;
     // Sets an address' code