diff --git a/include/evmc/evmc.h b/include/evmc/evmc.h
index a3b8fb4..40730e0 100644
--- a/include/evmc/evmc.h
+++ b/include/evmc/evmc.h
@@ -153,6 +153,7 @@ struct evmc_tx_context
     int64_t block_timestamp;         /**< The block timestamp. */
     int64_t block_gas_limit;         /**< The block gas limit. */
     evmc_uint256be block_difficulty; /**< The block difficulty. */
+    evmc_uint256be chain_id;         /**< The blockchain's ChainID. */
 };
 
 struct evmc_context;
diff --git a/include/evmc/evmc.hpp b/include/evmc/evmc.hpp
index ff486a2..4806e04 100644
--- a/include/evmc/evmc.hpp
+++ b/include/evmc/evmc.hpp
@@ -640,8 +640,7 @@ inline void emit_log(evmc_context* h,
 
 constexpr evmc_host_interface interface{
     account_exists, get_storage,  set_storage, get_balance,    get_code_size,  get_code_hash,
-    copy_code,      selfdestruct, call,        get_tx_context, get_block_hash, emit_log,
-};
+    copy_code,      selfdestruct, call,        get_tx_context, get_block_hash, emit_log};
 }  // namespace internal
 
 inline Host::Host() noexcept : evmc_context{&evmc::internal::interface} {}
diff --git a/include/evmc/instructions.h b/include/evmc/instructions.h
index 557fce7..84e9cbe 100644
--- a/include/evmc/instructions.h
+++ b/include/evmc/instructions.h
@@ -78,6 +78,7 @@ enum evmc_opcode
     OP_NUMBER = 0x43,
     OP_DIFFICULTY = 0x44,
     OP_GASLIMIT = 0x45,
+    OP_CHAINID = 0x46,
 
     OP_POP = 0x50,
     OP_MLOAD = 0x51,
diff --git a/lib/instructions/instruction_metrics.c b/lib/instructions/instruction_metrics.c
index 178c591..03a494f 100644
--- a/lib/instructions/instruction_metrics.c
+++ b/lib/instructions/instruction_metrics.c
@@ -92,7 +92,7 @@ static struct evmc_instruction_metrics istanbul_metrics[256] = {
     /*         NUMBER = 0x43 */ {BASE, 0, 1},
     /*     DIFFICULTY = 0x44 */ {BASE, 0, 1},
     /*       GASLIMIT = 0x45 */ {BASE, 0, 1},
-    /*                = 0x46 */ {UNDEFINED, 0, 0},
+    /*       CHAINID  = 0x46 */ {BASE, 0, 1},
     /*                = 0x47 */ {UNDEFINED, 0, 0},
     /*                = 0x48 */ {UNDEFINED, 0, 0},
     /*                = 0x49 */ {UNDEFINED, 0, 0},
diff --git a/lib/instructions/instruction_names.c b/lib/instructions/instruction_names.c
index 2f08fc1..361cfc8 100644
--- a/lib/instructions/instruction_names.c
+++ b/lib/instructions/instruction_names.c
@@ -76,7 +76,7 @@ static const char* istanbul_names[256] = {
     /* 0x43 */ "NUMBER",
     /* 0x44 */ "DIFFICULTY",
     /* 0x45 */ "GASLIMIT",
-    /* 0x46 */ NULL,
+    /* 0x46 */ "CHAINID",
     /* 0x47 */ NULL,
     /* 0x48 */ NULL,
     /* 0x49 */ NULL,
diff --git a/test/unittests/test_instructions.cpp b/test/unittests/test_instructions.cpp
index 0925c28..f60f910 100644
--- a/test/unittests/test_instructions.cpp
+++ b/test/unittests/test_instructions.cpp
@@ -251,7 +251,21 @@ TEST(instructions, istanbul_hard_fork)
 
     for (int op{OP_STOP}; op <= OP_SELFDESTRUCT; ++op)
     {
-        EXPECT_EQ(i[op], p[op]) << op;
-        EXPECT_STREQ(in[op], pn[op]) << op;
+        switch (op)
+        {
+        case OP_CHAINID:
+            continue;
+        default:
+            EXPECT_EQ(i[op], p[op]) << op;
+            EXPECT_STREQ(in[op], pn[op]) << op;
+            break;
+        }
     }
+
+    EXPECT_EQ(i[OP_CHAINID].gas_cost, 2);
+    EXPECT_EQ(i[OP_CHAINID].num_stack_arguments, 0);
+    EXPECT_EQ(i[OP_CHAINID].num_stack_returned_items, 1);
+    EXPECT_EQ(p[OP_CHAINID].gas_cost, -1);
+    EXPECT_EQ(in[OP_CHAINID], std::string{"CHAINID"});
+    EXPECT_TRUE(pn[OP_CHAINID] == nullptr);
 }