diff --git a/eg/debian/parse-rfc822.hy b/eg/debian/parse-rfc822.hy
index fe76870..3ba7de9 100644
--- a/eg/debian/parse-rfc822.hy
+++ b/eg/debian/parse-rfc822.hy
@@ -16,7 +16,7 @@
 (defn parse-rfc822-stream [fd]
   "Parse an RFC822 stream"
   (setv bits {})
-  (setv key null)
+  (setv key None)
   (for [line fd]
     (if (in ":" line)
         (do (setv line (.split line ":" 1))
diff --git a/hy/compiler.py b/hy/compiler.py
index f9aeac4..d71c5df 100644
--- a/hy/compiler.py
+++ b/hy/compiler.py
@@ -81,7 +81,7 @@ def load_stdlib():
 # keywords in Python 3.*
 def _is_hy_builtin(name, module_name):
     extras = ['True', 'False', 'None',
-              'true', 'false', 'nil', 'null']
+              'true', 'false', 'nil']
     if name in extras or keyword.iskeyword(name):
         return True
     # for non-Hy modules, check for pre-existing name in
@@ -459,8 +459,9 @@ class HyASTCompiler(object):
                 try:
                     value = next(exprs_iter)
                 except StopIteration:
-                    msg = "Keyword argument {kw} needs a value"
-                    raise HyCompileError(msg.format(kw=str(expr)))
+                    raise HyTypeError(expr,
+                                      "Keyword argument {kw} needs "
+                                      "a value.".format(kw=str(expr[1:])))
 
                 compiled_value = self.compile(value)
                 ret += compiled_value
@@ -2011,6 +2012,10 @@ class HyASTCompiler(object):
         result = self.compile(result)
         ld_name = self.compile(name)
 
+        if isinstance(ld_name.expr, ast.Call):
+            raise HyTypeError(name,
+                              "Can't assign to a callable: `%s'" % str_name)
+
         if result.temp_variables \
            and isinstance(name, HyString) \
            and '.' not in name:
diff --git a/hy/lex/parser.py b/hy/lex/parser.py
index a63be3e..abce1d7 100644
--- a/hy/lex/parser.py
+++ b/hy/lex/parser.py
@@ -289,7 +289,6 @@ def t_identifier(p):
         "true": "True",
         "false": "False",
         "nil": "None",
-        "null": "None",
     }
 
     if obj in table:
@@ -308,6 +307,9 @@ def t_identifier(p):
         if p.endswith("?") and p != "?":
             p = "is_%s" % (p[:-1])
 
+        if p.endswith("!") and p != "!":
+            p = "%s_bang" % (p[:-1])
+
         return p
 
     obj = ".".join([mangle(part) for part in obj.split(".")])
diff --git a/tests/compilers/test_ast.py b/tests/compilers/test_ast.py
index 69e5e15..54dc8d4 100644
--- a/tests/compilers/test_ast.py
+++ b/tests/compilers/test_ast.py
@@ -219,8 +219,8 @@ def test_ast_good_defclass():
 def test_ast_bad_defclass():
     "Make sure AST can't compile invalid defclass"
     cant_compile("(defclass)")
-    cant_compile("(defclass a null)")
-    cant_compile("(defclass a null null)")
+    cant_compile("(defclass a None)")
+    cant_compile("(defclass a None None)")
 
 
 def test_ast_good_lambda():
@@ -439,6 +439,16 @@ def test_lambda_list_keywords_mixed():
                     "  (list x xs kwxs kwoxs))")
 
 
+def test_missing_keyword_argument_value():
+    """Ensure the compiler chokes on missing keyword argument values."""
+    try:
+        can_compile("((fn [x] x) :x)")
+    except HyTypeError as e:
+        assert(e.message == "Keyword argument :x needs a value.")
+    else:
+        assert(False)
+
+
 def test_ast_unicode_strings():
     """Ensure we handle unicode strings correctly"""
 
@@ -527,3 +537,17 @@ def test_invalid_list_comprehension():
     cant_compile("(genexpr [x [1 2 3 4]] x)")
     cant_compile("(list-comp None [])")
     cant_compile("(list-comp [x [1 2 3]] x)")
+
+
+def test_bad_setv():
+    """Ensure setv handles error cases"""
+    cant_compile("(setv if 1)")
+    cant_compile("(setv (a b) [1 2])")
+
+
+def test_defn():
+    """Ensure that defn works correctly in various corner cases"""
+    cant_compile("(defn if [] 1)")
+    cant_compile("(defn \"hy\" [] 1)")
+    cant_compile("(defn :hy [] 1)")
+    can_compile("(defn &hy [] 1)")
diff --git a/tests/lex/test_lex.py b/tests/lex/test_lex.py
index cc95675..56ed52a 100644
--- a/tests/lex/test_lex.py
+++ b/tests/lex/test_lex.py
@@ -326,6 +326,24 @@ def test_lex_mangling_qmark():
     assert entry == [HySymbol(".is_foo.bar.is_baz")]
 
 
+def test_lex_mangling_bang():
+    """Ensure that identifiers ending with a bang get mangled ok"""
+    entry = tokenize("foo!")
+    assert entry == [HySymbol("foo_bang")]
+    entry = tokenize("!")
+    assert entry == [HySymbol("!")]
+    entry = tokenize("im!foo")
+    assert entry == [HySymbol("im!foo")]
+    entry = tokenize(".foo!")
+    assert entry == [HySymbol(".foo_bang")]
+    entry = tokenize("foo.bar!")
+    assert entry == [HySymbol("foo.bar_bang")]
+    entry = tokenize("foo!.bar")
+    assert entry == [HySymbol("foo_bang.bar")]
+    entry = tokenize(".foo!.bar.baz!")
+    assert entry == [HySymbol(".foo_bang.bar.baz_bang")]
+
+
 def test_simple_cons():
     """Check that cons gets tokenized correctly"""
     entry = tokenize("(a . b)")[0]
diff --git a/tests/native_tests/language.hy b/tests/native_tests/language.hy
index d468533..c6ae19b 100644
--- a/tests/native_tests/language.hy
+++ b/tests/native_tests/language.hy
@@ -54,8 +54,6 @@
        (except [e [TypeError]] (assert (in "Can't assign to a builtin" (str e)))))
   (try (eval '(setv nil 1))
        (except [e [TypeError]] (assert (in "Can't assign to a builtin" (str e)))))
-  (try (eval '(setv null 1))
-       (except [e [TypeError]] (assert (in "Can't assign to a builtin" (str e)))))
   (try (eval '(defn defclass [] (print "hello")))
        (except [e [TypeError]] (assert (in "Can't assign to a builtin" (str e)))))
   (try (eval '(defn get [] (print "hello")))
@@ -228,7 +226,7 @@
   "NATIVE: test if cond sorta works."
   (cond
    [(= 1 2) (assert (is true false))]
-   [(is null null) (setv x true) (assert x)]))
+   [(is None None) (setv x true) (assert x)]))
 
 
 (defn test-index []
@@ -673,6 +671,12 @@
   (assert (= 43 (my-fun 42))))
 
 
+(defn test-defn-lambdakey []
+  "NATIVE: test defn with a &symbol function name"
+  (defn &hy [] 1)
+  (assert (= (&hy) 1)))
+
+
 (defn test-defn-do []
   "NATIVE: test defn evaluation order with do"
   (setv acc [])
diff --git a/tests/native_tests/unless.hy b/tests/native_tests/unless.hy
index 2b957fe..a55e052 100644
--- a/tests/native_tests/unless.hy
+++ b/tests/native_tests/unless.hy
@@ -3,8 +3,8 @@
   (assert (= (unless false 1) 1))
   (assert (= (unless false 1 2) 2))
   (assert (= (unless false 1 3) 3))
-  (assert (= (unless true 2) null))
+  (assert (= (unless true 2) None))
   (assert (= (unless true 2) nil))
-  (assert (= (unless (!= 1 2) 42) null))
+  (assert (= (unless (!= 1 2) 42) None))
   (assert (= (unless (!= 1 2) 42) nil))
   (assert (= (unless (!= 2 2) 42) 42)))
diff --git a/tests/native_tests/when.hy b/tests/native_tests/when.hy
index c281439..9c21c9f 100644
--- a/tests/native_tests/when.hy
+++ b/tests/native_tests/when.hy
@@ -3,8 +3,8 @@
   (assert (= (when true 1) 1))
   (assert (= (when true 1 2) 2))
   (assert (= (when true 1 3) 3))
-  (assert (= (when false 2) null))
-  (assert (= (when (= 1 2) 42) null))
+  (assert (= (when false 2) None))
+  (assert (= (when (= 1 2) 42) None))
   (assert (= (when false 2) nil))
   (assert (= (when (= 1 2) 42) nil))
   (assert (= (when (= 2 2) 42) 42)))