diff --git a/core/id_kind.py b/core/id_kind.py
index 47f06ce0e5..abddf8a266 100755
--- a/core/id_kind.py
+++ b/core/id_kind.py
@@ -384,11 +384,15 @@ def AddKinds(spec):
 
     'NotTilde',  # !~
 
+    # TODO: We could use the same Dummy for all?
     'WordsDummy',    # Used for @() (words in lex_mode_e.ShCommand)
     'CommandDummy',  # Used for $() (command in lex_mode_e.ShCommand)
     'DqDummy',       # Used for ""
     'SqDummy',       # Used for ''
 
+    # Constants
+    'Null', 'True', 'False',
+
     # Keywords are resolved after lexing, but otherwise behave like tokens.
     # NOTE: These are not used because pgen2 automatically creates a
     # gr.keywords dict in the grammar.
diff --git a/frontend/lex.py b/frontend/lex.py
index f15c994cbb..c7559a7c2e 100644
--- a/frontend/lex.py
+++ b/frontend/lex.py
@@ -822,6 +822,12 @@ def IsKeyword(name):
 
 # NOTE: Borrowing tokens from Arith (i.e. $(( )) ), but not using LexerPairs().
 LEXER_DEF[lex_mode_e.Expr] = _OIL_LEFT_SUBS + _OIL_LEFT_UNQUOTED + [
+  # NOTE: pgen2 is taking care of 'in', 'is', etc.?  Should we register those?
+  # We probably want those too.
+  C('null', Id.Expr_Null),
+  C('true', Id.Expr_True),
+  C('false', Id.Expr_False),
+
   # These can be looked up as keywords separately, so you enforce that they have
   # space around them?
   R(VAR_NAME_RE, Id.Expr_Name),
diff --git a/oil_lang/expr_eval.py b/oil_lang/expr_eval.py
index 73e915bfca..fe43b161c7 100644
--- a/oil_lang/expr_eval.py
+++ b/oil_lang/expr_eval.py
@@ -93,7 +93,15 @@ def EvalExpr(self, node):
       print('')
 
     if node.tag == expr_e.Const:
-      return int(node.c.val)
+      id_ = node.c.id
+      if id_ == Id.Expr_Digits:
+        return int(node.c.val)
+      elif id_ == Id.Expr_Null:
+        return None
+      elif id_ == Id.Expr_True:
+        return True
+      elif id_ == Id.Expr_False:
+        return False
 
     if node.tag == expr_e.Var:
       return self.LookupVar(node.name.val)
diff --git a/oil_lang/expr_to_ast.py b/oil_lang/expr_to_ast.py
index d995943aa7..a92972f079 100644
--- a/oil_lang/expr_to_ast.py
+++ b/oil_lang/expr_to_ast.py
@@ -316,8 +316,11 @@ def Expr(self, pnode):
 
       if tok.id == Id.Expr_Name:
         return expr.Var(tok)
+      # TODO: Should I combine all of these?
       elif tok.id == Id.Expr_Digits:
         return expr.Const(tok)
+      elif tok.id in (Id.Expr_Null, Id.Expr_True, Id.Expr_False):
+        return expr.Const(tok)
 
       else:
         raise AssertionError(tok.id)
diff --git a/oil_lang/grammar.pgen2 b/oil_lang/grammar.pgen2
index 4e2fc369dd..cfad474243 100644
--- a/oil_lang/grammar.pgen2
+++ b/oil_lang/grammar.pgen2
@@ -113,7 +113,7 @@ atom_expr: ['await'] atom trailer*
 atom: ('(' [yield_expr|testlist_comp] ')' |
        '[' [testlist_comp] ']' |
        '{' [dictorsetmaker] '}' |
-       NAME | NUMBER | '...' | 'None' | 'True' | 'False' |
+       NAME | NUMBER | '...' | Expr_Null | Expr_True | Expr_False |
        array_literal | sh_array_literal |
        command_sub | sh_command_sub |
        regex_literal |
diff --git a/spec/oil-expr.test.sh b/spec/oil-expr.test.sh
index 8bf694befc..3710cf3a93 100644
--- a/spec/oil-expr.test.sh
+++ b/spec/oil-expr.test.sh
@@ -367,3 +367,29 @@ bar
 foo
 bar
 ## END
+
+#### null / true / false
+shopt -s all:oil
+var n = null
+if (n) {
+  echo yes
+} else {
+  echo no
+}
+var t = true
+if (t) {
+  echo yes
+} else {
+  echo no
+}
+var f = false
+if (f) {
+  echo yes
+} else {
+  echo no
+}
+## STDOUT:
+no
+yes
+no
+## END