diff --git a/artiq/py2llvm/builtins.py b/artiq/py2llvm/builtins.py
index daa94c70a..90e222374 100644
--- a/artiq/py2llvm/builtins.py
+++ b/artiq/py2llvm/builtins.py
@@ -1,6 +1,6 @@
 """
-The :mod:`builtins` module contains the builtin Python and ARTIQ
-types, such as int or float.
+The :mod:`builtins` module contains the builtin Python
+and ARTIQ types, such as int or float.
 """
 
 from . import types
@@ -32,16 +32,16 @@ class TList(types.TMono):
         super().__init__("list", {"elt": elt})
 
 def fn_len():
-    return types.TBuiltin("len")
+    return types.TBuiltin("function len")
 
 def fn_round():
-    return types.TBuiltin("round")
+    return types.TBuiltin("function round")
 
 def fn_range():
-    return types.TBuiltin("range")
+    return types.TBuiltin("function range")
 
 def fn_syscall():
-    return types.TBuiltin("syscall")
+    return types.TBuiltin("function syscall")
 
 # Accessors
 
@@ -79,3 +79,8 @@ def is_collection(typ):
     typ = typ.find()
     return isinstance(typ, types.TTuple) or \
         types.is_mono(typ, "list")
+
+def is_function(typ, name):
+    typ = typ.find()
+    return isinstance(typ, types.TBuiltin) and \
+        typ.name == "function " + name
diff --git a/artiq/py2llvm/prelude.py b/artiq/py2llvm/prelude.py
new file mode 100644
index 000000000..4e4d93fe7
--- /dev/null
+++ b/artiq/py2llvm/prelude.py
@@ -0,0 +1,17 @@
+"""
+The :mod:`prelude` module contains the initial global environment
+in which ARTIQ kernels are evaluated.
+"""
+
+from . import builtins
+
+def globals():
+    return {
+        "bool":    builtins.TBool(),
+        "int":     builtins.TInt(),
+        "float":   builtins.TFloat(),
+        "round":   builtins.fn_round(),
+        "len":     builtins.fn_len(),
+        "range":   builtins.fn_range(),
+        "syscall": builtins.fn_syscall(),
+    }
diff --git a/artiq/py2llvm/typing.py b/artiq/py2llvm/typing.py
index 3ceae8eb3..676dce879 100644
--- a/artiq/py2llvm/typing.py
+++ b/artiq/py2llvm/typing.py
@@ -24,7 +24,7 @@ class LocalExtractor(algorithm.Visitor):
         # parameters can't be declared as global or nonlocal
         self.params     = set()
 
-        if len(self.env_stack) == 0:
+        if len(self.env_stack) == 1:
             self.env_stack.append(self.typing_env)
 
     def visit_in_assign(self, node):
@@ -115,7 +115,7 @@ class LocalExtractor(algorithm.Visitor):
 
             self.global_.add(name)
             self._assignable(name)
-            self.env_stack[0][name] = self.typing_env[name]
+            self.env_stack[1][name] = self.typing_env[name]
 
     def visit_Nonlocal(self, node):
         for name, loc in zip(node.names, node.name_locs):
@@ -123,9 +123,9 @@ class LocalExtractor(algorithm.Visitor):
                     self._check_not_in(name, self.params, "a parameter", "nonlocal", loc):
                 continue
 
-            # nonlocal does not search global scope
+            # nonlocal does not search prelude and global scopes
             found = False
-            for outer_env in reversed(self.env_stack[1:]):
+            for outer_env in reversed(self.env_stack[2:]):
                 if name in outer_env:
                     found = True
                     break
@@ -156,9 +156,9 @@ class ASTTypedRewriter(algorithm.Transformer):
     via :class:`LocalExtractor`.
     """
 
-    def __init__(self, engine):
+    def __init__(self, engine, globals={}):
         self.engine = engine
-        self.env_stack = []
+        self.env_stack = [globals]
 
     def _find_name(self, name, loc):
         for typing_env in reversed(self.env_stack):
@@ -990,6 +990,7 @@ class Printer(algorithm.Visitor):
 
 def main():
     import sys, fileinput, os
+    from . import prelude
 
     if len(sys.argv) > 1 and sys.argv[1] == '+diag':
         del sys.argv[1]
@@ -1009,7 +1010,7 @@ def main():
     buf = source.Buffer("".join(fileinput.input()).expandtabs(),
                         os.path.basename(fileinput.filename()))
     parsed, comments = parse_buffer(buf, engine=engine)
-    typed = ASTTypedRewriter(engine=engine).visit(parsed)
+    typed = ASTTypedRewriter(globals=prelude.globals(), engine=engine).visit(parsed)
     Inferencer(engine=engine).visit(typed)
 
     printer = Printer(buf)
diff --git a/lit-test/py2llvm/typing/prelude.py b/lit-test/py2llvm/typing/prelude.py
new file mode 100644
index 000000000..d1229f66c
--- /dev/null
+++ b/lit-test/py2llvm/typing/prelude.py
@@ -0,0 +1,10 @@
+# RUN: %python -m artiq.py2llvm.typing %s >%t
+# RUN: OutputCheck %s --file-to-check=%t
+
+# CHECK-L: x:<built-in function len>
+x = len
+
+def f():
+    global len
+    # CHECK-L: len:int(width='a) =
+    len = 1