diff --git a/tests/functional/syntax/test_abi_decode.py b/tests/functional/syntax/test_abi_decode.py
index e566babae0..19935f8cba 100644
--- a/tests/functional/syntax/test_abi_decode.py
+++ b/tests/functional/syntax/test_abi_decode.py
@@ -1,7 +1,7 @@
 import pytest
 
 from vyper import compiler
-from vyper.exceptions import TypeMismatch
+from vyper.exceptions import CompilerPanic, TypeMismatch, UnfoldableNode
 
 fail_list = [
     (
@@ -31,13 +31,31 @@ def test_abi_decode_fail(bad_code, exc):
         compiler.compile_code(bad_code)
 
 
-valid_list = ["""
+valid_list = [
+    """
 @external
 def foo(x: Bytes[32]) -> uint256:
     return _abi_decode(x, uint256)
-    """]
+    """,
+    """
+@external
+def foo(x: Bytes[32]) -> uint256:
+    return _abi_decode(x, uint256, unwrap_tuple=(0 < 1))
+    """,
+]
 
 
 @pytest.mark.parametrize("good_code", valid_list)
 def test_abi_decode_success(good_code):
     assert compiler.compile_code(good_code) is not None
+
+
+# UnfoldableNode on legacy, CompilerPanic in venom
+@pytest.mark.xfail(raises=(UnfoldableNode, CompilerPanic))
+def test_abi_decode_unwrap_tuple_foldable_expr():
+    code = """
+@external
+def f(x: Bytes[32]) -> uint256:
+    return abi_decode(x, uint256, unwrap_tuple=empty(bool))
+    """
+    assert compiler.compile_code(code) is not None
diff --git a/tests/functional/syntax/test_abi_encode.py b/tests/functional/syntax/test_abi_encode.py
index edb441652a..0f1d2ebfcb 100644
--- a/tests/functional/syntax/test_abi_encode.py
+++ b/tests/functional/syntax/test_abi_encode.py
@@ -1,7 +1,7 @@
 import pytest
 
 from vyper import compiler
-from vyper.exceptions import InvalidLiteral, TypeMismatch
+from vyper.exceptions import InvalidLiteral, TypeMismatch, UnfoldableNode
 
 fail_list = [
     (
@@ -119,9 +119,24 @@ def foo(x: Bytes[1]) -> Bytes[68]:
 def foo() -> Bytes[224]:
     return _abi_encode(BAR)
     """,
+    """
+@external
+def foo(x: Bytes[1]) -> Bytes[96]:
+    return _abi_encode(x, ensure_tuple=(0 < 1))
+    """,
 ]
 
 
 @pytest.mark.parametrize("good_code", valid_list)
 def test_abi_encode_success(good_code):
     assert compiler.compile_code(good_code) is not None
+
+
+@pytest.mark.xfail(raises=UnfoldableNode)
+def test_abi_encode_ensure_tuple_foldable_expr():
+    code = """
+@external
+def f(x: uint256) -> Bytes[64]:
+    return abi_encode(x, ensure_tuple=empty(bool))
+    """
+    assert compiler.compile_code(code) is not None
diff --git a/vyper/builtins/functions.py b/vyper/builtins/functions.py
index 2e773f10dc..4bbc30c409 100644
--- a/vyper/builtins/functions.py
+++ b/vyper/builtins/functions.py
@@ -108,15 +108,20 @@
 
 
 class FoldedFunctionT(BuiltinFunctionT):
-    # Base class for nodes which should always be folded
+    """
+    Base class for nodes which should always be folded
+    """
 
     _modifiability = Modifiability.CONSTANT
 
 
 class TypenameFoldedFunctionT(FoldedFunctionT):
-    # Base class for builtin functions that:
-    # (1) take a typename as the only argument; and
-    # (2) should always be folded.
+    """
+    Base class for builtin functions that:
+    (1) take a typename as the only argument; and
+    (2) should always be folded.
+    """
+
     _inputs = [("typename", TYPE_T.any())]
 
     def fetch_call_return(self, node):
@@ -2243,11 +2248,14 @@ def infer_kwarg_types(self, node):
 
     def fetch_call_return(self, node):
         self._validate_arg_types(node)
-        ensure_tuple = next(
-            (arg.value.value for arg in node.keywords if arg.arg == "ensure_tuple"), True
-        )
+        kwargs = {kw.arg: kw.value for kw in node.keywords}
+
+        if "ensure_tuple" in kwargs:
+            ensure_tuple = kwargs["ensure_tuple"].get_folded_value().value
+        else:
+            ensure_tuple = True
+
         assert isinstance(ensure_tuple, bool)
-        has_method_id = "method_id" in [arg.arg for arg in node.keywords]
 
         # figure out the output type by converting
         # the types to ABI_Types and calling size_bound API
@@ -2264,7 +2272,7 @@ def fetch_call_return(self, node):
 
         maxlen = arg_abi_t.size_bound()
 
-        if has_method_id:
+        if "method_id" in kwargs:
             # the output includes 4 bytes for the method_id.
             maxlen += 4