diff --git a/bigframes/core/compile/ibis_compiler/scalar_op_registry.py b/bigframes/core/compile/ibis_compiler/scalar_op_registry.py
index e8a2b0b6ce..635ba516e4 100644
--- a/bigframes/core/compile/ibis_compiler/scalar_op_registry.py
+++ b/bigframes/core/compile/ibis_compiler/scalar_op_registry.py
@@ -1173,6 +1173,10 @@ def udf(*inputs):
 
 @scalar_op_compiler.register_unary_op(ops.MapOp, pass_op=True)
 def map_op_impl(x: ibis_types.Value, op: ops.MapOp):
+    # this should probably be handled by a rewriter
+    if len(op.mappings) == 0:
+        return x
+
     case = ibis_api.case()
     for mapping in op.mappings:
         case = case.when(x == mapping[0], mapping[1])
diff --git a/bigframes/core/compile/sqlglot/expressions/generic_ops.py b/bigframes/core/compile/sqlglot/expressions/generic_ops.py
index 8a792c0753..6a3825309c 100644
--- a/bigframes/core/compile/sqlglot/expressions/generic_ops.py
+++ b/bigframes/core/compile/sqlglot/expressions/generic_ops.py
@@ -78,6 +78,8 @@ def _(expr: TypedExpr) -> sge.Expression:
 
 @register_unary_op(ops.MapOp, pass_op=True)
 def _(expr: TypedExpr, op: ops.MapOp) -> sge.Expression:
+    if len(op.mappings) == 0:
+        return expr.expr
     return sge.Case(
         this=expr.expr,
         ifs=[
diff --git a/tests/system/small/test_series.py b/tests/system/small/test_series.py
index d1a252f8dc..65b170df32 100644
--- a/tests/system/small/test_series.py
+++ b/tests/system/small/test_series.py
@@ -733,10 +733,12 @@ def test_series_replace_nans_with_pd_na(scalars_dfs):
     (
         ({"Hello, World!": "Howdy, Planet!", "T": "R"},),
         ({},),
+        ({0: "Hello, World!"},),
     ),
     ids=[
         "non-empty",
         "empty",
+        "off-type",
     ],
 )
 def test_series_replace_dict(scalars_dfs, replacement_dict):