diff --git a/crates/fe/tests/fixtures/fe_test_runner/assert_msg.fe b/crates/fe/tests/fixtures/fe_test_runner/assert_msg.fe
new file mode 100644
index 0000000000..37a97e6b75
--- /dev/null
+++ b/crates/fe/tests/fixtures/fe_test_runner/assert_msg.fe
@@ -0,0 +1,53 @@
+use std::evm::{Address, Call, Create, Evm, RawMem, last_returndata}
+use std::evm::mem
+
+#[test(should_revert, selector = 0x08c379a0)]
+fn test_assert_msg_reverts() uses (evm: mut Evm) {
+    assert_msg(false, "boom")
+}
+
+#[test]
+fn test_assert_msg_passes() uses (evm: mut Evm) {
+    assert_msg(true, "should not revert")
+}
+
+msg ReverterMsg {
+    #[selector = 0xaabbccdd]
+    Trigger,
+}
+
+pub contract Reverter {
+    recv ReverterMsg {
+        Trigger {} {
+            assert_msg(false, "boom")
+        }
+    }
+}
+
+#[test]
+fn test_assert_msg_payload_layout() uses (evm: mut Evm) {
+    let addr = evm.create2<Reverter>(value: 0, args: (), salt: 0)
+
+    // Build calldata containing only the ReverterMsg::Trigger selector.
+    let selector_word = (0xaabbccdd as u256) << 224
+    let ptr = mem::alloc(4)
+    evm.mstore(addr: ptr, value: selector_word)
+
+    let ok = evm.raw_call(addr: addr, gas: 100000, value: 0, args_offset: ptr, args_len: 4)
+    assert(!ok)
+
+    // Solidity `Error(string)` for "boom":
+    //   selector(4) | offset = 0x20 (32) | len = 4 (32) | "boom" right-padded (32) = 100
+    // Catches the bug where assert_msg encodes the bare `Text` payload
+    // (`len || bytes`) instead of the single-arg tuple `(message,)`
+    // (`offset || len || bytes`).
+    let ret = last_returndata()
+    assert(ret.len == 100)
+    assert(evm.mload(ret.base) >> 224 == 0x08c379a0)
+    assert(evm.mload(ret.base + 4) == 0x20)
+    assert(evm.mload(ret.base + 36) == 4)
+    assert(
+        evm.mload(ret.base + 68)
+            == 0x626f6f6d00000000000000000000000000000000000000000000000000000000,
+    )
+}
diff --git a/crates/fe/tests/fixtures/fe_test_runner/assert_msg.snap b/crates/fe/tests/fixtures/fe_test_runner/assert_msg.snap
new file mode 100644
index 0000000000..d7ce3e3be4
--- /dev/null
+++ b/crates/fe/tests/fixtures/fe_test_runner/assert_msg.snap
@@ -0,0 +1,13 @@
+---
+source: crates/fe/tests/cli_output.rs
+expression: output
+input_file: tests/fixtures/fe_test_runner/assert_msg.fe
+---
+=== STDOUT ===
+PASS  [<time>] test_assert_msg_reverts
+PASS  [<time>] test_assert_msg_passes
+PASS  [<time>] test_assert_msg_payload_layout
+
+test result: ok. 3 passed; 0 failed
+
+=== EXIT CODE: 0 ===
diff --git a/crates/language-server/test_files/completion.snap b/crates/language-server/test_files/completion.snap
index 55fd5a5711..e3cc4ac035 100644
--- a/crates/language-server/test_files/completion.snap
+++ b/crates/language-server/test_files/completion.snap
@@ -45,6 +45,7 @@ completions:
   - Vec (Class)
   - another_func_with_args (Function) -> "another_func_with_args(${1:x}, ${2:y})$0" [fn another_func_with_args(x: i32, y: i32) -> i32]
   - assert (Function) -> "assert(${1:b})$0" [fn assert(b: bool)]
+  - assert_msg (Function) -> "assert_msg(${1:b}, ${2:message})$0" [fn assert_msg(b: bool, message: DynString)]
   - func_with_args (Function) -> "func_with_args(${1:x}, ${2:y})$0" [use utils::func_with_args [fn func_with_args(x: i32, y: i32) -> i32]] {+0:use utils::func_with_args}
   - help (Function) -> "help()$0" [use utils::help [fn help() -> i32]] {+0:use utils::help}
   - helper_func (Function) -> "helper_func()$0" [use utils::helper_func [fn helper_func() -> i32]] {+0:use utils::helper_func}
@@ -114,6 +115,7 @@ completions:
   - Some (EnumMember)
   - another_func_with_args (Function) -> "another_func_with_args(${1:x}, ${2:y})$0" [fn another_func_with_args(x: i32, y: i32) -> i32]
   - assert (Function) -> "assert(${1:b})$0" [fn assert(b: bool)]
+  - assert_msg (Function) -> "assert_msg(${1:b}, ${2:message})$0" [fn assert_msg(b: bool, message: DynString)]
   - func_with_args (Function) -> "func_with_args(${1:x}, ${2:y})$0" [use utils::func_with_args [fn func_with_args(x: i32, y: i32) -> i32]] {+0:use utils::func_with_args}
   - help (Function) -> "help()$0" [use utils::help [fn help() -> i32]] {+0:use utils::help}
   - helper_func (Function) -> "helper_func()$0" [use utils::helper_func [fn helper_func() -> i32]] {+0:use utils::helper_func}
@@ -178,6 +180,7 @@ completions:
   - Some (EnumMember)
   - another_func_with_args (Function) -> "another_func_with_args(${1:x}, ${2:y})$0" [fn another_func_with_args(x: i32, y: i32) -> i32]
   - assert (Function) -> "assert(${1:b})$0" [fn assert(b: bool)]
+  - assert_msg (Function) -> "assert_msg(${1:b}, ${2:message})$0" [fn assert_msg(b: bool, message: DynString)]
   - func_with_args (Function) -> "func_with_args(${1:x}, ${2:y})$0" [use utils::func_with_args [fn func_with_args(x: i32, y: i32) -> i32]] {+0:use utils::func_with_args}
   - help (Function) -> "help()$0" [use utils::help [fn help() -> i32]] {+0:use utils::help}
   - helper_func (Function) -> "helper_func()$0" [use utils::helper_func [fn helper_func() -> i32]] {+0:use utils::helper_func}
diff --git a/crates/language-server/test_files/goto_contract.snap b/crates/language-server/test_files/goto_contract.snap
index 8c53dd71b6..a463ceb841 100644
--- a/crates/language-server/test_files/goto_contract.snap
+++ b/crates/language-server/test_files/goto_contract.snap
@@ -1,6 +1,5 @@
 ---
 source: crates/language-server/src/functionality/goto.rs
-assertion_line: 456
 expression: snapshot
 input_file: test_files/goto_contract.fe
 ---
@@ -104,25 +103,25 @@ note:
    ┌─ goto_contract.fe:70:5
    │
 70 │     Mint { to: u256, amount: u256 } -> bool,
-   │     ^^^^ -> goto_contract::TokenMsg::Mint
+   │     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -> goto_contract::TokenMsg::Mint
 
 note: 
    ┌─ goto_contract.fe:71:5
    │
 71 │     GetSupply -> u256,
-   │     ^^^^^^^^^ -> goto_contract::TokenMsg::GetSupply
+   │     ^^^^^^^^^^^^^^^^^ -> goto_contract::TokenMsg::GetSupply
 
 note: 
    ┌─ goto_contract.fe:75:5
    │
 75 │     SetOwner { new_owner: u256 } -> bool,
-   │     ^^^^^^^^ -> goto_contract::AdminMsg::SetOwner
+   │     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -> goto_contract::AdminMsg::SetOwner
 
 note: 
    ┌─ goto_contract.fe:76:5
    │
 76 │     GetOwner -> u256,
-   │     ^^^^^^^^ -> goto_contract::AdminMsg::GetOwner
+   │     ^^^^^^^^^^^^^^^^ -> goto_contract::AdminMsg::GetOwner
 
 note: 
    ┌─ goto_contract.fe:81:31
diff --git a/crates/language-server/test_files/goto_effects.snap b/crates/language-server/test_files/goto_effects.snap
index 855d16fab4..02124f3436 100644
--- a/crates/language-server/test_files/goto_effects.snap
+++ b/crates/language-server/test_files/goto_effects.snap
@@ -217,13 +217,13 @@ note:
    ┌─ goto_effects.fe:71:5
    │
 71 │     Add { x: u256 } -> u256,
-   │     ^^^ -> goto_effects::CalcMsg::Add
+   │     ^^^^^^^^^^^^^^^^^^^^^^^ -> goto_effects::CalcMsg::Add
 
 note: 
    ┌─ goto_effects.fe:72:5
    │
 72 │     GetState -> u256,
-   │     ^^^^^^^^ -> goto_effects::CalcMsg::GetState
+   │     ^^^^^^^^^^^^^^^^ -> goto_effects::CalcMsg::GetState
 
 note: 
    ┌─ goto_effects.fe:75:40
diff --git a/crates/language-server/test_files/hoverable/src/lib.snap b/crates/language-server/test_files/hoverable/src/lib.snap
index fa185ccffb..02ee765cba 100644
--- a/crates/language-server/test_files/hoverable/src/lib.snap
+++ b/crates/language-server/test_files/hoverable/src/lib.snap
@@ -669,17 +669,31 @@ note:
 97 │ │ }
    │ ╰─^ def: defined here @ 92:0 (11 refs)
 
+note: 
+   ┌─ lib.fe:93:3
+   │  
+93 │ ╭   #[selector = 0x01]
+94 │ │   Mint { to: i32, amount: i32 } -> bool,
+   │ ╰───────────────────────────────────────^ ref: 93:2
+
 note: 
    ┌─ lib.fe:94:3
    │
 94 │   Mint { to: i32, amount: i32 } -> bool,
-   │   ^^^^ ref: 94:2
+   │   ^^^^ def: defined here @ 94:2 (13 refs)
+
+note: 
+   ┌─ lib.fe:95:3
+   │  
+95 │ ╭   #[selector = 0x02]
+96 │ │   Burn { amount: i32 } -> bool,
+   │ ╰──────────────────────────────^ ref: 95:2
 
 note: 
    ┌─ lib.fe:96:3
    │
 96 │   Burn { amount: i32 } -> bool,
-   │   ^^^^ ref: 96:2
+   │   ^^^^ def: defined here @ 96:2 (13 refs)
 
 note: 
    ┌─ lib.fe:99:14
diff --git a/crates/language-server/test_files/hoverable/src/stuff.snap b/crates/language-server/test_files/hoverable/src/stuff.snap
index 767bf54447..ffe409abb8 100644
--- a/crates/language-server/test_files/hoverable/src/stuff.snap
+++ b/crates/language-server/test_files/hoverable/src/stuff.snap
@@ -669,17 +669,31 @@ note:
 97 │ │ }
    │ ╰─^ def: defined here @ 92:0 (11 refs)
 
+note: 
+   ┌─ lib.fe:93:3
+   │  
+93 │ ╭   #[selector = 0x01]
+94 │ │   Mint { to: i32, amount: i32 } -> bool,
+   │ ╰───────────────────────────────────────^ ref: 93:2
+
 note: 
    ┌─ lib.fe:94:3
    │
 94 │   Mint { to: i32, amount: i32 } -> bool,
-   │   ^^^^ ref: 94:2
+   │   ^^^^ def: defined here @ 94:2 (13 refs)
+
+note: 
+   ┌─ lib.fe:95:3
+   │  
+95 │ ╭   #[selector = 0x02]
+96 │ │   Burn { amount: i32 } -> bool,
+   │ ╰──────────────────────────────^ ref: 95:2
 
 note: 
    ┌─ lib.fe:96:3
    │
 96 │   Burn { amount: i32 } -> bool,
-   │   ^^^^ ref: 96:2
+   │   ^^^^ def: defined here @ 96:2 (13 refs)
 
 note: 
    ┌─ lib.fe:99:14
diff --git a/crates/uitest/fixtures/ty_check/event_unsupported_field_type.snap b/crates/uitest/fixtures/ty_check/event_unsupported_field_type.snap
index 748cf4569a..e2b20ee731 100644
--- a/crates/uitest/fixtures/ty_check/event_unsupported_field_type.snap
+++ b/crates/uitest/fixtures/ty_check/event_unsupported_field_type.snap
@@ -12,9 +12,9 @@ error[6-0003]: trait bound is not satisfied
   6 │ │ }
     │ ╰─^ `StorageMap<Address, u256, 0>` doesn't implement `Encode<Sol>`
     │
-    ┌─ src/evm/effects.fe:343:14
+    ┌─ src/evm/effects.fe:344:14
     │
-343 │     where T: Encode<Sol> + AbiSize
+344 │     where T: Encode<Sol> + AbiSize
     │              ----------- required by this bound on `encode_abi_payload`
 
 error[6-0003]: trait bound is not satisfied
@@ -26,7 +26,7 @@ error[6-0003]: trait bound is not satisfied
   6 │ │ }
     │ ╰─^ `StorageMap<Address, u256, 0>` doesn't implement `AbiSize`
     │
-    ┌─ src/evm/effects.fe:343:28
+    ┌─ src/evm/effects.fe:344:28
     │
-343 │     where T: Encode<Sol> + AbiSize
+344 │     where T: Encode<Sol> + AbiSize
     │                            ------- required by this bound on `encode_abi_payload`
diff --git a/ingots/std/src/evm/effects.fe b/ingots/std/src/evm/effects.fe
index d62b428d4a..fb004d45e3 100644
--- a/ingots/std/src/evm/effects.fe
+++ b/ingots/std/src/evm/effects.fe
@@ -20,6 +20,7 @@ use ingot::evm::intrinsic::{
     code_region_offset as intrinsic_code_region_offset,
 }
 use ingot::abi::Sol
+use ingot::abi::Text
 use ingot::abi::sol::{decode_input_at, decode_output}
 use super::calldata::CallData
 use super::contract_field_slot
@@ -683,6 +684,19 @@ pub fn assert(_ b: own bool) {
     if !b { revert_error(Panic { code: 0x01 }) }
 }
 
+/// Assert with a Solidity-compatible `Error(string)` revert message.
+///
+/// When `b` is false, reverts with the 4-byte selector `0x08c379a0`
+/// (keccak256("Error(string)")[..4]) followed by the ABI-encoded
+/// message, matching Solidity's `require(cond, "message")` / `revert("message")`.
+pub fn assert_msg(_ b: own bool, _ message: own Text) {
+    if !b {
+        // Error(string) has one ABI argument, so encode the full argument list.
+        let (ptr, len) = encode_calldata(0x08c379a0, (message,))
+        ops::revert(offset: ptr, len: len)
+    }
+}
+
 /// Revert the current transaction with ABI-encoded data.
 ///
 /// Encodes the given value using Solidity ABI encoding and reverts
diff --git a/ingots/std/src/prelude.fe b/ingots/std/src/prelude.fe
index b77e41ab3e..67013760c2 100644
--- a/ingots/std/src/prelude.fe
+++ b/ingots/std/src/prelude.fe
@@ -6,4 +6,4 @@ pub use core::abi::{Abi, AbiEncoder, AbiSize, Encode}
 pub use super::abi::{Sol, Text, Vec}
 
 // Common EVM types.
-pub use super::evm::{Evm, Address, Call, Ctx, StorageMap, Create, Log, Panic, assert, revert, revert_error}
+pub use super::evm::{Evm, Address, Call, Ctx, StorageMap, Create, Log, Panic, assert, assert_msg, revert, revert_error}
diff --git a/newsfragments/1348.feature.md b/newsfragments/1348.feature.md
new file mode 100644
index 0000000000..c877dfff85
--- /dev/null
+++ b/newsfragments/1348.feature.md
@@ -0,0 +1 @@
+Added `assert_msg(cond, message)`, which reverts with a Solidity-compatible `Error(string)` payload (selector `0x08c379a0`) when `cond` is false.