diff --git a/README.md b/README.md
index 0e58539..7061648 100644
--- a/README.md
+++ b/README.md
@@ -79,7 +79,6 @@ These features of Shopify Liquid aren't implemented:
   }}`. [[Issue #42](https://github.com/osteele/liquid/issues/42)]
 - Warn and lax [error modes](https://github.com/shopify/liquid#error-modes).
 - Non-strict filters. An undefined filter is currently an error.
-- Strict variables. An undefined variable is not an error.
 
 ### Drops
 
diff --git a/cmd/liquid/main.go b/cmd/liquid/main.go
index 74ec7ae..2151290 100644
--- a/cmd/liquid/main.go
+++ b/cmd/liquid/main.go
@@ -21,12 +21,13 @@ import (
 
 // for testing
 var (
-	stderr   io.Writer              = os.Stderr
-	stdout   io.Writer              = os.Stdout
-	stdin    io.Reader              = os.Stdin
-	exit     func(int)              = os.Exit
-	env      func() []string        = os.Environ
-	bindings map[string]interface{} = map[string]interface{}{}
+	stderr     io.Writer              = os.Stderr
+	stdout     io.Writer              = os.Stdout
+	stdin      io.Reader              = os.Stdin
+	exit       func(int)              = os.Exit
+	env        func() []string        = os.Environ
+	bindings   map[string]interface{} = map[string]interface{}{}
+	strictVars bool
 )
 
 func main() {
@@ -41,6 +42,7 @@ func main() {
 
 	var bindEnvs bool
 	cmdLine.BoolVar(&bindEnvs, "env", false, "bind environment variables")
+	cmdLine.BoolVar(&strictVars, "strict", false, "enable strict variable mode in templates")
 
 	err = cmdLine.Parse(os.Args[1:])
 	if err != nil {
@@ -86,7 +88,11 @@ func render() error {
 		return err
 	}
 
-	tpl, err := liquid.NewEngine().ParseTemplate(buf)
+	e := liquid.NewEngine()
+	if strictVars {
+		e.StrictVariables()
+	}
+	tpl, err := e.ParseTemplate(buf)
 	if err != nil {
 		return err
 	}
diff --git a/cmd/liquid/main_test.go b/cmd/liquid/main_test.go
index aba0753..565a697 100644
--- a/cmd/liquid/main_test.go
+++ b/cmd/liquid/main_test.go
@@ -58,6 +58,7 @@ func TestMain(t *testing.T) {
 	main()
 	require.True(t, envCalled)
 	require.Equal(t, "Hello, World!", buf.String())
+	bindings = make(map[string]interface{})
 
 	// filename
 	stdin = os.Stdin
@@ -72,6 +73,17 @@ func TestMain(t *testing.T) {
 	exitCode := 0
 	exit = func(n int) { exitCalled = true; exitCode = n }
 
+	// strict variables
+	stdin = bytes.NewBufferString(src)
+	buf = &bytes.Buffer{}
+	stderr = buf
+	os.Args = []string{"liquid", "--strict"}
+	main()
+	require.True(t, exitCalled)
+	require.Equal(t, 1, exitCode)
+	require.Equal(t, "Liquid error: undefined variable in {{ TARGET }}\n", buf.String())
+
+	exitCode = 0
 	os.Args = []string{"liquid", "testdata/source.liquid"}
 	main()
 	require.Equal(t, 0, exitCode)
diff --git a/engine.go b/engine.go
index bcc1295..69f38f4 100644
--- a/engine.go
+++ b/engine.go
@@ -66,6 +66,11 @@ func (e *Engine) RegisterTag(name string, td Renderer) {
 	})
 }
 
+// StrictVariables causes the renderer to error when the template contains an undefined variable.
+func (e *Engine) StrictVariables() {
+	e.cfg.StrictVariables = true
+}
+
 // ParseTemplate creates a new Template using the engine configuration.
 func (e *Engine) ParseTemplate(source []byte) (*Template, SourceError) {
 	return newTemplate(&e.cfg, source, "", 0)
diff --git a/render/config.go b/render/config.go
index 65ec55b..afc8f51 100644
--- a/render/config.go
+++ b/render/config.go
@@ -8,7 +8,8 @@ import (
 type Config struct {
 	parser.Config
 	grammar
-	Cache map[string][]byte
+	Cache           map[string][]byte
+	StrictVariables bool
 }
 
 type grammar struct {
diff --git a/render/render.go b/render/render.go
index 3e8b812..c072eb4 100644
--- a/render/render.go
+++ b/render/render.go
@@ -2,6 +2,7 @@
 package render
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"reflect"
@@ -66,6 +67,9 @@ func (n *ObjectNode) render(w *trimWriter, ctx nodeContext) Error {
 	if err != nil {
 		return wrapRenderError(err, n)
 	}
+	if value == nil && ctx.config.StrictVariables {
+		return wrapRenderError(errors.New("undefined variable"), n)
+	}
 	if err := wrapRenderError(writeObject(w, value), n); err != nil {
 		return err
 	}
diff --git a/render/render_test.go b/render/render_test.go
index db8d334..57b1b62 100644
--- a/render/render_test.go
+++ b/render/render_test.go
@@ -52,6 +52,23 @@ var renderTests = []struct{ in, out string }{
 	{`x {%- y -%} z`, "xyz"},
 }
 
+var renderStrictTests = []struct{ in, out string }{
+	// literal representations
+	{`{{ true }}`, "true"},
+	{`{{ false }}`, "false"},
+	{`{{ 12 }}`, "12"},
+	{`{{ 12.3 }}`, "12.3"},
+	{`{{ date }}`, "2015-07-17 15:04:05 +0000"},
+	{`{{ "string" }}`, "string"},
+	{`{{ array }}`, "firstsecondthird"},
+
+	// variables and properties
+	{`{{ int }}`, "123"},
+	{`{{ page.title }}`, "Introduction"},
+	{`{{ array[1] }}`, "second"},
+	{`{{ invalid }}`, ""},
+}
+
 var renderErrorTests = []struct{ in, out string }{
 	{`{% errblock %}{% enderrblock %}`, "errblock error"},
 }
@@ -111,6 +128,26 @@ func TestRenderErrors(t *testing.T) {
 	}
 }
 
+func TestRenderStrictVariables(t *testing.T) {
+	cfg := NewConfig()
+	cfg.StrictVariables = true
+	addRenderTestTags(cfg)
+	for i, test := range renderStrictTests {
+		t.Run(fmt.Sprintf("%02d", i+1), func(t *testing.T) {
+			root, err := cfg.Compile(test.in, parser.SourceLoc{})
+			require.NoErrorf(t, err, test.in)
+			buf := new(bytes.Buffer)
+			err = Render(root, buf, renderTestBindings, cfg)
+			if test.in == `{{ invalid }}` {
+				require.Errorf(t, err, test.in)
+			} else {
+				require.NoErrorf(t, err, test.in)
+			}
+			require.Equalf(t, test.out, buf.String(), test.in)
+		})
+	}
+}
+
 func addRenderTestTags(cfg Config) {
 	cfg.AddTag("y", func(string) (func(io.Writer, Context) error, error) {
 		return func(w io.Writer, _ Context) error {