diff --git a/tests/functional/builtins/codegen/test_convert.py b/tests/functional/builtins/codegen/test_convert.py
index 9947223e75..1c11938d50 100644
--- a/tests/functional/builtins/codegen/test_convert.py
+++ b/tests/functional/builtins/codegen/test_convert.py
@@ -662,6 +662,36 @@ def foo() -> {t_bytes}:
     assert c2.foo() == test_data
 
 
+@pytest.mark.parametrize("n", range(1, 32))
+def test_literal_bytestrings_to_bytes_m(get_contract, n):
+    test_data = "1" * n
+    out = test_data.encode()
+
+    bytes_m_typ = f"bytes{n}"
+    contract_1 = f"""
+@external
+def foo() -> {bytes_m_typ}:
+    return convert(b"{test_data}", {bytes_m_typ})
+
+@external
+def bar() -> {bytes_m_typ}:
+    return convert("{test_data}", {bytes_m_typ})
+    """
+
+    contract_2 = f"""
+@external
+def fubar(x: String[{n}]) -> {bytes_m_typ}:
+    return convert(x, {bytes_m_typ})
+    """
+
+    c1 = get_contract(contract_1)
+    assert c1.foo() == out
+    assert c1.bar() == out
+
+    with pytest.raises(TypeMismatch):
+        compile_code(contract_2)
+
+
 @pytest.mark.parametrize("i_typ,o_typ,val", generate_reverting_cases())
 @pytest.mark.fuzzing
 def test_conversion_failures(get_contract, assert_compile_failed, tx_failed, i_typ, o_typ, val):
diff --git a/tests/functional/syntax/test_constants.py b/tests/functional/syntax/test_constants.py
index db2accf359..5cec6492cb 100644
--- a/tests/functional/syntax/test_constants.py
+++ b/tests/functional/syntax/test_constants.py
@@ -324,6 +324,17 @@ def foo(): nonpayable
 FOO: constant(Foo) = Foo(BAR)
 BAR: constant(address) = 0xFFfFfFffFFfffFFfFFfFFFFFffFFFffffFfFFFfF
     """,
+    # conversion of literal bytestrings to bytes_M
+    """
+b: constant(bytes5) = convert(b"vyper", bytes5)
+    """,
+    """
+b: constant(bytes5) = convert("vyper", bytes5)
+    """,
+    """
+a: constant(Bytes[5]) = b"vyper"
+b: constant(bytes5) = convert(a, bytes5)
+    """,
 ]
 
 
diff --git a/vyper/builtins/_convert.py b/vyper/builtins/_convert.py
index a494e4a344..00cde54a36 100644
--- a/vyper/builtins/_convert.py
+++ b/vyper/builtins/_convert.py
@@ -363,20 +363,34 @@ def to_decimal(expr, arg, out_typ):
         raise CompilerPanic("unreachable")
 
 
-@_input_types(IntegerT, DecimalT, BytesM_T, AddressT, BytesT, BoolT)
+@_input_types(IntegerT, DecimalT, BytesM_T, AddressT, BytesT, StringT, BoolT)
 def to_bytes_m(expr, arg, out_typ):
     _check_bytes(expr, arg, out_typ, max_bytes_allowed=out_typ.m)
 
-    if isinstance(arg.typ, BytesT):
-        bytes_val = LOAD(bytes_data_ptr(arg))
-
-        # zero out any dirty bytes (which can happen in the last
-        # word of a bytearray)
-        len_ = get_bytearray_length(arg)
-        num_zero_bits = IRnode.from_list(["mul", ["sub", 32, len_], 8])
-        with num_zero_bits.cache_when_complex("bits") as (b, num_zero_bits):
-            arg = shl(num_zero_bits, shr(num_zero_bits, bytes_val))
-            arg = b.resolve(arg)
+    if isinstance(arg.typ, _BytestringT):
+        # handle literal bytestrings first
+        if isinstance(expr, vy_ast.Constant) and arg.typ.length <= out_typ.m:
+            val = expr.value
+            if isinstance(arg.typ, StringT):
+                val = val.encode("utf-8")
+
+            # bytes_m types are left padded with zeros
+            val = int(val.hex(), 16) << 8 * (out_typ.m - arg.typ.length)
+            arg = shl(256 - out_typ.m_bits, val)
+
+        elif isinstance(arg.typ, BytesT):
+            bytes_val = LOAD(bytes_data_ptr(arg))
+
+            # zero out any dirty bytes (which can happen in the last
+            # word of a bytearray)
+            len_ = get_bytearray_length(arg)
+            num_zero_bits = IRnode.from_list(["mul", ["sub", 32, len_], 8])
+            with num_zero_bits.cache_when_complex("bits") as (b, num_zero_bits):
+                arg = shl(num_zero_bits, shr(num_zero_bits, bytes_val))
+                arg = b.resolve(arg)
+
+        else:
+            _FAIL(arg.typ, out_typ, expr)
 
     elif is_bytes_m_type(arg.typ):
         # clamp if it's a downcast
diff --git a/vyper/builtins/functions.py b/vyper/builtins/functions.py
index 629ab684a8..979fcd8b53 100644
--- a/vyper/builtins/functions.py
+++ b/vyper/builtins/functions.py
@@ -55,6 +55,7 @@
 )
 from vyper.semantics.analysis.base import Modifiability, VarInfo
 from vyper.semantics.analysis.utils import (
+    check_modifiability,
     get_common_types,
     get_exact_type_from_node,
     get_possible_types_from_node,
@@ -194,6 +195,9 @@ def build_IR(self, expr, args, kwargs, context):
 class Convert(BuiltinFunctionT):
     _id = "convert"
 
+    def check_modifiability_for_call(self, node, modifiability):
+        return check_modifiability(node.args[0], modifiability)
+
     def fetch_call_return(self, node):
         _, target_typedef = self.infer_arg_types(node)