diff --git a/src/puya/arc32.py b/src/puya/arc32.py
index 5d8f44503a..a89b598be7 100644
--- a/src/puya/arc32.py
+++ b/src/puya/arc32.py
@@ -6,6 +6,8 @@
 from puya import log
 from puya.errors import InternalError
 from puya.models import (
+    ABIMethodArgConstantDefault,
+    ABIMethodArgDefault,
     ARC4ABIMethod,
     ARC4BareMethod,
     ARC4CreateOption,
@@ -91,26 +93,27 @@ def _get_signature(method: ARC4ABIMethod) -> str:
 
 
 def _encode_default_arg(
-    metadata: ContractMetaData, source: str, loc: SourceLocation | None
+    metadata: ContractMetaData, source: ABIMethodArgDefault, loc: SourceLocation | None
 ) -> JSONDict:
-    if state := metadata.global_state.get(source):
+    if isinstance(source, ABIMethodArgConstantDefault):
+        return {"source": "constant", "data": source.value}
+    if state := metadata.global_state.get(source.name):
         return {
             "source": "global-state",
             # TODO: handle non utf-8 bytes
             "data": state.key.decode("utf-8"),
         }
-    if state := metadata.local_state.get(source):
+    if state := metadata.local_state.get(source.name):
         return {
             "source": "local-state",
             "data": state.key.decode("utf-8"),
         }
     for method in metadata.arc4_methods:
-        if isinstance(method, ARC4ABIMethod) and method.name == source:
+        if isinstance(method, ARC4ABIMethod) and method.name == source.name:
             return {
                 "source": "abi-method",
                 "data": _encode_abi_method(method),
             }
-    # TODO: constants
     raise InternalError(f"Cannot find source '{source}' on {metadata.ref}", loc)
 
 
diff --git a/src/puya/ir/arc4_router.py b/src/puya/ir/arc4_router.py
index 9b235a57d4..9ba95bbebf 100644
--- a/src/puya/ir/arc4_router.py
+++ b/src/puya/ir/arc4_router.py
@@ -9,6 +9,7 @@
 )
 from puya.errors import CodeError, InternalError
 from puya.models import (
+    ABIMethodArgConstantDefault,
     ARC4ABIMethod,
     ARC4ABIMethodConfig,
     ARC4BareMethod,
@@ -480,7 +481,7 @@ def _validate_default_args(
         args_by_name = {a.name: a for a in method.args}
         for (
             parameter_name,
-            source_name,
+            default_source,
         ) in method.arc4_method_config.default_args.items():
             # any invalid parameter matches should have been caught earlier
             parameter = args_by_name[parameter_name]
@@ -492,6 +493,17 @@ def _validate_default_args(
                 case "account":
                     param_arc4_type = "address"
 
+            if isinstance(default_source, ABIMethodArgConstantDefault):
+                if not _is_valid_client_literal_for_arc4_type(
+                    default_source.value, param_arc4_type
+                ):
+                    logger.warning(
+                        f"'{default_source.value}' is not a valid"
+                        f" default value for parameter '{parameter_name}'"
+                    )
+                continue
+
+            source_name = default_source.name
             try:
                 source = known_sources[source_name]
             except KeyError as ex:
@@ -681,6 +693,18 @@ def _get_abi_signature(subroutine: awst_nodes.ContractMethod, config: ARC4ABIMet
     return f"{config.name}({','.join(arg_types)}){return_type}"
 
 
+def _is_valid_client_literal_for_arc4_type(literal: str | int, arc4_type_alias: str) -> bool:
+    if arc4_type_alias.startswith(("uint", "ufixed")):
+        return isinstance(literal, int)
+
+    match arc4_type_alias:
+        case "byte" | "bool":
+            return isinstance(literal, int)
+        case "address" | "string":
+            return isinstance(literal, str)
+    return False
+
+
 def _wtype_to_arc4(wtype: wtypes.WType, loc: SourceLocation | None = None) -> str:
     match wtype:
         case wtypes.ARC4Type(arc4_name=arc4_name):
diff --git a/src/puya/models.py b/src/puya/models.py
index f469b9b591..36e99e5987 100644
--- a/src/puya/models.py
+++ b/src/puya/models.py
@@ -66,6 +66,19 @@ class ARC4BareMethodConfig:
     create: ARC4CreateOption = ARC4CreateOption.disallow
 
 
+@attrs.frozen(kw_only=True)
+class ABIMethodArgConstantDefault:
+    value: int | str
+
+
+@attrs.frozen(kw_only=True)
+class ABIMethodArgMemberDefault:
+    name: str
+
+
+ABIMethodArgDefault = ABIMethodArgMemberDefault | ABIMethodArgConstantDefault
+
+
 @attrs.frozen(kw_only=True)
 class ARC4ABIMethodConfig:
     source_location: SourceLocation
@@ -77,7 +90,7 @@ class ARC4ABIMethodConfig:
     create: ARC4CreateOption = ARC4CreateOption.disallow
     name: str
     readonly: bool = False
-    default_args: immutabledict[str, str] = immutabledict()
+    default_args: immutabledict[str, ABIMethodArgDefault] = immutabledict()
     """Mapping is from parameter -> source"""
     structs: immutabledict[str, ARC32StructDef] = immutabledict()
 
diff --git a/src/puyapy/awst_build/arc4_utils.py b/src/puyapy/awst_build/arc4_utils.py
index 7cee4f749e..c232226e79 100644
--- a/src/puyapy/awst_build/arc4_utils.py
+++ b/src/puyapy/awst_build/arc4_utils.py
@@ -12,6 +12,8 @@
 from puya.awst import wtypes
 from puya.errors import CodeError, InternalError
 from puya.models import (
+    ABIMethodArgDefault,
+    ABIMethodArgMemberDefault,
     ARC4ABIMethodConfig,
     ARC4BareMethodConfig,
     ARC4CreateOption,
@@ -183,7 +185,7 @@ def get_arc4_abimethod_data(
             readonly = default_readonly
 
     # map "default_args" param
-    default_args = dict[str, str]()
+    default_args = dict[str, ABIMethodArgDefault]()
     match evaluated_args.pop("default_args", {}):
         case {**options}:
             method_arg_names = func_types.keys() - {"output"}
@@ -198,7 +200,7 @@ def get_arc4_abimethod_data(
                 else:
                     # if it's in method_arg_names, it's a str
                     assert isinstance(parameter, str)
-                    default_args[parameter] = value
+                    default_args[parameter] = ABIMethodArgMemberDefault(name=value)
         case invalid_default_args_option:
             context.error(f"invalid default_args option: {invalid_default_args_option}", dec_loc)