diff --git a/artiq/transforms/inline.py b/artiq/transforms/inline.py
index 5e7591a0e..1f3a63d9c 100644
--- a/artiq/transforms/inline.py
+++ b/artiq/transforms/inline.py
@@ -1,4 +1,4 @@
-from collections import namedtuple, defaultdict
+from collections import namedtuple
 from fractions import Fraction
 import inspect
 import textwrap
@@ -10,6 +10,26 @@ from artiq.language import core as core_language
 from artiq.language import units
 
 
+class _HostObjectMapper:
+    def __init__(self, first_encoding=0):
+        self._next_encoding = first_encoding
+        # id(object) -> (encoding, object)
+        # this format is required to support non-hashable host objects.
+        self._d = dict()
+
+    def encode(self, obj):
+        try:
+            return self._d[id(obj)][0]
+        except KeyError:
+            encoding = self._next_encoding
+            self._d[id(obj)] = (encoding, obj)
+            self._next_encoding += 1
+            return encoding
+
+    def get_map(self):
+        return {encoding: obj for i, (encoding, obj) in self._d.items()}
+
+
 _UserVariable = namedtuple("_UserVariable", "name")
 
 
@@ -20,8 +40,9 @@ class _ReferenceManager:
         self.to_inlined = dict()
         # inlined_name -> use_count
         self.use_count = dict()
-        self.rpc_map = defaultdict(lambda: len(self.rpc_map))
-        self.exception_map = defaultdict(lambda: len(self.exception_map))
+        self.rpc_mapper = _HostObjectMapper()
+        # exceptions 0-1023 are for runtime
+        self.exception_mapper = _HostObjectMapper(1024)
         self.kernel_attr_init = []
 
         # reserved names
@@ -83,13 +104,19 @@ class _ReferenceManager:
             raise NotImplementedError
 
 
-_embeddable_calls = {
+_embeddable_calls = (
     core_language.delay, core_language.at, core_language.now,
     core_language.syscall,
     range, int, float, round,
     core_language.int64, core_language.round64, core_language.array,
     Fraction, units.Quantity, core_language.EncodedException
-}
+)
+
+def _is_embeddable(call):
+    for ec in _embeddable_calls:
+        if call is ec:
+            return True
+    return False
 
 
 class _ReferenceReplacer(ast.NodeVisitor):
@@ -156,7 +183,7 @@ class _ReferenceReplacer(ast.NodeVisitor):
         func = self.rm.get(self.obj, self.func_name, node.func)
         new_args = [self.visit(arg) for arg in node.args]
 
-        if func in _embeddable_calls:
+        if _is_embeddable(func):
             new_func = ast.Name(func.__name__, ast.Load())
             return ast.copy_location(
                 ast.Call(func=new_func, args=new_args,
@@ -177,7 +204,7 @@ class _ReferenceReplacer(ast.NodeVisitor):
                 body=inlined.body))
             return ast.copy_location(ast.Name(retval_name, ast.Load()), node)
         else:
-            args = [ast.Str("rpc"), value_to_ast(self.rm.rpc_map[func])]
+            args = [ast.Str("rpc"), value_to_ast(self.rm.rpc_mapper.encode(func))]
             args += new_args
             return ast.copy_location(
                 ast.Call(func=ast.Name("syscall", ast.Load()),
@@ -216,7 +243,7 @@ class _ReferenceReplacer(ast.NodeVisitor):
             exception_class = self.rm.get(self.obj, self.func_name, node.exc)
             if not inspect.isclass(exception_class):
                 raise NotImplementedError("Exception must be a class")
-            exception_id = self.rm.exception_map[exception_class]
+            exception_id = self.rm.exception_mapper.encode(exception_class)
             node.exc = ast.copy_location(
                     ast.Call(func=ast.Name("EncodedException", ast.Load()),
                              args=[value_to_ast(exception_id)],
@@ -228,7 +255,7 @@ class _ReferenceReplacer(ast.NodeVisitor):
         exception_class = self.rm.get(self.obj, self.func_name, e)
         if not inspect.isclass(exception_class):
             raise NotImplementedError("Exception type must be a class")
-        exception_id = self.rm.exception_map[exception_class]
+        exception_id = self.rm.exception_mapper.encode(exception_class)
         return ast.copy_location(
             ast.Call(func=ast.Name("EncodedException", ast.Load()),
                      args=[value_to_ast(exception_id)],
@@ -302,9 +329,4 @@ def inline(core, k_function, k_args, k_kwargs, rm=None, retval_name=None):
     if init_kernel_attr:
         func_def.body[0:0] = rm.kernel_attr_init
 
-    r_rpc_map = dict((rpc_num, rpc_fun)
-                     for rpc_fun, rpc_num in rm.rpc_map.items())
-    r_exception_map = dict((exception_num, exception_class)
-                           for exception_class, exception_num
-                           in rm.exception_map.items())
-    return func_def, r_rpc_map, r_exception_map
+    return func_def, rm.rpc_mapper.get_map(), rm.exception_mapper.get_map()