diff --git a/src/aeso_ast_infer_types.erl b/src/aeso_ast_infer_types.erl
index ae6fb16..a3455eb 100644
--- a/src/aeso_ast_infer_types.erl
+++ b/src/aeso_ast_infer_types.erl
@@ -380,7 +380,8 @@ global_env() ->
                      {"RelativeTTL", Fun1(Int, TTL)},
                      {"FixedTTL",    Fun1(Int, TTL)},
                      %% Abort
-                     {"abort", Fun1(String, A)}])
+                     {"abort", Fun1(String, A)},
+                     {"require", Fun([Bool, String], A)}])
         , types = MkDefs(
                     [{"int", 0}, {"bool", 0}, {"char", 0}, {"string", 0}, {"address", 0},
                      {"hash", {[], {alias_t, Bytes(32)}}},
diff --git a/src/aeso_ast_to_fcode.erl b/src/aeso_ast_to_fcode.erl
index e7cb013..6948b3d 100644
--- a/src/aeso_ast_to_fcode.erl
+++ b/src/aeso_ast_to_fcode.erl
@@ -170,7 +170,7 @@ builtins() ->
     MkName = fun(NS, Fun) ->
                 list_to_atom(string:to_lower(string:join(NS ++ [Fun], "_")))
              end,
-    Scopes = [{[],           [{"abort", 1}]},
+    Scopes = [{[],           [{"abort", 1}, {"require", 2}]},
               {["Chain"],    [{"spend", 2}, {"balance", 1}, {"block_hash", 1}, {"coinbase", none},
                               {"timestamp", none}, {"block_height", none}, {"difficulty", none},
                               {"gas_limit", none}]},
@@ -765,6 +765,8 @@ op_builtins() ->
      bits_difference, int_to_str, address_to_str, crypto_ecverify,
      crypto_ecverify_secp256k1, crypto_sha3, crypto_sha256, crypto_blake2b].
 
+builtin_to_fcode(require, [Cond, Msg]) ->
+    make_if(Cond, {tuple, []}, {builtin, abort, [Msg]});
 builtin_to_fcode(map_delete, [Key, Map]) ->
     {op, map_delete, [Map, Key]};
 builtin_to_fcode(map_member, [Key, Map]) ->
diff --git a/src/aeso_ast_to_icode.erl b/src/aeso_ast_to_icode.erl
index d296f1a..24f9c05 100644
--- a/src/aeso_ast_to_icode.erl
+++ b/src/aeso_ast_to_icode.erl
@@ -174,6 +174,8 @@ ast_body({qid, _, [Con, "put"]}, #{ contract_name := Con }) ->
 %% Abort
 ast_body(?id_app("abort", [String], _, _), Icode) ->
     builtin_call(abort, [ast_body(String, Icode)]);
+ast_body(?id_app("require", [Bool, String], _, _), Icode) ->
+    builtin_call(require, [ast_body(Bool, Icode), ast_body(String, Icode)]);
 
 %% Authentication
 ast_body({qid, _, ["Auth", "tx_hash"]}, _Icode) ->
diff --git a/src/aeso_builtins.erl b/src/aeso_builtins.erl
index b94cb79..bd4010c 100644
--- a/src/aeso_builtins.erl
+++ b/src/aeso_builtins.erl
@@ -45,6 +45,7 @@ builtin_deps1({baseX_int, X})             -> [{baseX_int_pad, X}];
 builtin_deps1({baseX_int_pad, X})         -> [{baseX_int_encode, X}];
 builtin_deps1({baseX_int_encode, X})      -> [{baseX_int_encode_, X}, {baseX_tab, X}, {baseX_digits, X}];
 builtin_deps1(string_reverse)             -> [string_reverse_];
+builtin_deps1(require)                    -> [abort];
 builtin_deps1(_)                          -> [].
 
 dep_closure(Deps) ->
@@ -131,6 +132,7 @@ builtin_function(BF) ->
     case BF of
         {event, EventT}            -> bfun(BF, builtin_event(EventT));
         abort                      -> bfun(BF, builtin_abort());
+        require                    -> bfun(BF, builtin_require());
         {map_lookup, Type}         -> bfun(BF, builtin_map_lookup(Type));
         map_put                    -> bfun(BF, builtin_map_put());
         map_delete                 -> bfun(BF, builtin_map_delete());
@@ -201,6 +203,11 @@ builtin_abort() ->
                    A(?REVERT)]}, %% Stack: 0,Ptr
      {tuple,[]}}.
 
+builtin_require() ->
+    {[{"c", word}, {"msg", string}],
+     {ifte, ?V(c), {tuple, []}, ?call(abort, [?V(msg)])},
+     {tuple, []}}.
+
 %% Map primitives
 builtin_map_lookup(Type) ->
     Ret = aeso_icode:option_typerep(Type),
diff --git a/test/contracts/aeproof.aes b/test/contracts/aeproof.aes
index 75006eb..53402b1 100644
--- a/test/contracts/aeproof.aes
+++ b/test/contracts/aeproof.aes
@@ -104,10 +104,10 @@ contract AEProof =
                      proofsByOwner : map(address, array(uint)) }
 
     function notarize(document:string, comment:string, ipfsHash:hash) =
-        let _ = require(aetoken.balanceOf(caller()) > 0)
+        let _ = require(aetoken.balanceOf(caller()) > 0, "false")
         let proofHash: uint = calculateHash(document)
         let proof : proof = Map.get_(proofHash, state().proofs)
-        let _ = require(proof.owner == #0)
+        let _ = require(proof.owner == #0, "false")
         let proof' : proof = proof { owner = caller()
                                    , timestamp = block().timestamp
                                    , proofBlock = block().height
@@ -124,12 +124,12 @@ contract AEProof =
     function getProof(document) : proof =
         let calcHash = calculateHash(document)
         let proof = Map.get_(calcHash, state().proofs)
-        let _ = require(proof.owner != #0)
+        let _ = require(proof.owner != #0, "false")
         proof
 
     function getProofByHash(hash: uint) : proof =
         let proof = Map.get_(hash, state().proofs)
-        let _ = require(proof.owner != #0)
+        let _ = require(proof.owner != #0, "false")
         proof
 
 
@@ -141,5 +141,3 @@ contract AEProof =
     function getProofsByOwner(owner: address): array(uint) =
         Map.get(owner, state())
 
-    function require(x : bool) : unit = if(x) () else abort("false")
-
diff --git a/test/contracts/basic_auth.aes b/test/contracts/basic_auth.aes
index 641c01e..3e2647f 100644
--- a/test/contracts/basic_auth.aes
+++ b/test/contracts/basic_auth.aes
@@ -15,5 +15,3 @@ contract BasicAuth =
   function to_sign(h : hash, n : int) =
     Crypto.blake2b((h, n))
 
-  private function require(b : bool, err : string) =
-    if(!b) abort(err)
diff --git a/test/contracts/bitcoin_auth.aes b/test/contracts/bitcoin_auth.aes
index ba60c31..9d421c8 100644
--- a/test/contracts/bitcoin_auth.aes
+++ b/test/contracts/bitcoin_auth.aes
@@ -14,5 +14,3 @@ contract BitcoinAuth =
   function to_sign(h : hash, n : int) : hash =
     Crypto.blake2b((h, n))
 
-  private function require(b : bool, err : string) =
-    if(!b) abort(err)
diff --git a/test/contracts/dutch_auction.aes b/test/contracts/dutch_auction.aes
index deca3ef..a9c5db0 100644
--- a/test/contracts/dutch_auction.aes
+++ b/test/contracts/dutch_auction.aes
@@ -15,9 +15,6 @@ contract DutchAuction =
     Chain.spend(to, amount)
     total - amount
 
-  private function require(b : bool, err : string) =
-    if(!b) abort(err)
-
   // TTL set by user on posting contract, typically (start - end ) div dec
   public function init(beneficiary, start, decrease) : state =
     require(start > 0 && decrease > 0, "bad args")
diff --git a/test/contracts/erc20_token.aes b/test/contracts/erc20_token.aes
index f2c5cca..517b9f4 100644
--- a/test/contracts/erc20_token.aes
+++ b/test/contracts/erc20_token.aes
@@ -77,9 +77,6 @@ contract ERC20Token =
     put( state{approval_log = e :: state.approval_log })
     e
 
-  private function require(b : bool, err : string) =
-    if(!b) abort(err)
-
   private function sub(_a : int, _b : int) : int =
     require(_b =< _a, "Error")
     _a - _b
diff --git a/test/contracts/fundme.aes b/test/contracts/fundme.aes
index 08f5d69..abae348 100644
--- a/test/contracts/fundme.aes
+++ b/test/contracts/fundme.aes
@@ -12,9 +12,6 @@ contract FundMe =
                    deadline      : int,
                    goal          : int }
 
-  private function require(b : bool, err : string) =
-    if(!b) abort(err)
-
   private stateful function spend(args : spend_args) =
     Chain.spend(args.recipient, args.amount)
 
diff --git a/test/contracts/oracles.aes b/test/contracts/oracles.aes
index e6e44b4..97561ff 100644
--- a/test/contracts/oracles.aes
+++ b/test/contracts/oracles.aes
@@ -108,5 +108,3 @@ contract Oracles =
     Oracle.respond(o, q, Answer(question, "magic", 1337), signature = sig)
     Oracle.get_answer(o, q)
 
-  private function require(b : bool, err : string) =
-    if(!b) abort(err)
diff --git a/test/contracts/oracles_gas.aes b/test/contracts/oracles_gas.aes
index 7e75a67..87c8b28 100644
--- a/test/contracts/oracles_gas.aes
+++ b/test/contracts/oracles_gas.aes
@@ -20,5 +20,3 @@ contract OraclesGas =
     Oracle.respond(o, q, answer)
     ()
 
-  private function require(b : bool, err : string) =
-    if(!b) abort(err)
diff --git a/test/contracts/oracles_no_vm.aes b/test/contracts/oracles_no_vm.aes
index ad32066..b0ba9ac 100644
--- a/test/contracts/oracles_no_vm.aes
+++ b/test/contracts/oracles_no_vm.aes
@@ -33,5 +33,3 @@ contract Oracles =
                      q : query_id) : option(answer_t) =
     Oracle.get_answer(o, q)
 
-  private function require(b : bool, err : string) =
-    if(!b) abort(err)
diff --git a/test/contracts/variant_types.aes b/test/contracts/variant_types.aes
index 59079c2..3d84161 100644
--- a/test/contracts/variant_types.aes
+++ b/test/contracts/variant_types.aes
@@ -9,8 +9,6 @@ contract VariantTypes =
 
   function init() = Stopped
 
-  function require(b) = if(!b) abort("required")
-
   stateful function start(bal : int) =
     switch(state)
       Stopped => put(Started({owner = Call.caller, balance = bal, color = Grey(0)}))
@@ -18,7 +16,7 @@ contract VariantTypes =
   stateful function stop() =
     switch(state)
       Started(st) =>
-        require(Call.caller == st.owner)
+        require(Call.caller == st.owner, "required")
         put(Stopped)
         st.balance