diff --git a/tfexec/cmd.go b/tfexec/cmd.go
index 5a3e38e2..f5457769 100644
--- a/tfexec/cmd.go
+++ b/tfexec/cmd.go
@@ -107,13 +107,13 @@ func (tf *Terraform) runTerraformCmd(cmd *exec.Cmd) error {
 
 	stdout := tf.stdout
 	if cmd.Stdout != nil {
-		stdout = io.MultiWriter(cmd.Stdout, stdout)
+		stdout = io.MultiWriter(stdout, cmd.Stdout)
 	}
 	cmd.Stdout = stdout
 
 	stderr := io.MultiWriter(&errBuf, tf.stderr)
 	if cmd.Stderr != nil {
-		stderr = io.MultiWriter(cmd.Stderr, stderr)
+		stderr = io.MultiWriter(stderr, cmd.Stderr)
 	}
 	cmd.Stderr = stderr
 
diff --git a/tfexec/errors.go b/tfexec/errors.go
index 22edbde9..933d5ba2 100644
--- a/tfexec/errors.go
+++ b/tfexec/errors.go
@@ -5,6 +5,20 @@ import (
 	"fmt"
 	"os/exec"
 	"regexp"
+	"strings"
+)
+
+var (
+	// The "Required variable not set:" case is for 0.11
+	missingVarErrRegexp  = regexp.MustCompile(`Error: No value for required variable|Error: Required variable not set:`)
+	missingVarNameRegexp = regexp.MustCompile(`The root module input variable "(.+)" is not set, and has no default|Error: Required variable not set: (.+)`)
+
+	usageRegexp = regexp.MustCompile(`Too many command line arguments|^Usage: .*Options:.*|Error: Invalid -\d+ option`)
+
+	// "Could not load plugin" is present in 0.13
+	noInitErrRegexp = regexp.MustCompile(`Error: Could not satisfy plugin requirements|Error: Could not load plugin`)
+
+	noConfigErrRegexp = regexp.MustCompile(`Error: No configuration files`)
 )
 
 func parseError(err error, stderr string) error {
@@ -13,16 +27,22 @@ func parseError(err error, stderr string) error {
 	}
 
 	switch {
-	// case ErrTerraformNotFound.regexp.MatchString(stderr):
-	// return ErrTerraformNotFound
-	case regexp.MustCompile(usageRegexp).MatchString(stderr):
+	case missingVarErrRegexp.MatchString(stderr):
+		name := ""
+		names := missingVarNameRegexp.FindStringSubmatch(stderr)
+		for i := 1; i < len(names); i++ {
+			name = strings.TrimSpace(names[i])
+			if name != "" {
+				break
+			}
+		}
+		
+		return &ErrMissingVar{name}
+	case usageRegexp.MatchString(stderr):
 		return &ErrCLIUsage{stderr: stderr}
-	case regexp.MustCompile(`Error: Could not satisfy plugin requirements`).MatchString(stderr):
-		return &ErrNoInit{stderr: stderr}
-	case regexp.MustCompile(`Error: Could not load plugin`).MatchString(stderr):
-		// this string is present in 0.13
+	case noInitErrRegexp.MatchString(stderr):
 		return &ErrNoInit{stderr: stderr}
-	case regexp.MustCompile(`Error: No configuration files`).MatchString(stderr):
+	case noConfigErrRegexp.MatchString(stderr):
 		return &ErrNoConfig{stderr: stderr}
 	default:
 		return errors.New(stderr)
@@ -77,8 +97,6 @@ type ErrCLIUsage struct {
 	stderr string
 }
 
-var usageRegexp = `Too many command line arguments|^Usage: .*Options:.*|Error: Invalid -\d+ option`
-
 func (e *ErrCLIUsage) Error() string {
 	return e.stderr
 }
@@ -92,3 +110,11 @@ type ErrManualEnvVar struct {
 func (err *ErrManualEnvVar) Error() string {
 	return fmt.Sprintf("manual setting of env var %q detected", err.name)
 }
+
+type ErrMissingVar struct {
+	VariableName string
+}
+
+func (err *ErrMissingVar) Error() string {
+	return fmt.Sprintf("variable %q was required but not supplied", err.VariableName)
+}
diff --git a/tfexec/internal/e2etest/errors_test.go b/tfexec/internal/e2etest/errors_test.go
index c25a1402..f71262c1 100644
--- a/tfexec/internal/e2etest/errors_test.go
+++ b/tfexec/internal/e2etest/errors_test.go
@@ -35,3 +35,30 @@ func TestUnparsedError(t *testing.T) {
 		}
 	})
 }
+
+func TestMissingVar(t *testing.T) {
+	runTest(t, "var", func(t *testing.T, tfv *version.Version, tf *tfexec.Terraform) {
+		err := tf.Init(context.Background())
+		if err != nil {
+			t.Fatalf("err during init: %s", err)
+		} 
+
+		err = tf.Plan(context.Background())
+		if err == nil {
+			t.Fatalf("expected error running Plan, none returned")
+		}
+		var e *tfexec.ErrMissingVar
+		if !errors.As(err, &e) {
+			t.Fatalf("expected ErrMissingVar, got %T, %s", err, err)
+		}
+
+		if e.VariableName != "no_default" {
+			t.Fatalf("expected missing no_default, got %q", e.VariableName)
+		}
+
+		err = tf.Plan(context.Background(), tfexec.Var("no_default=foo"))
+		if err != nil {
+			t.Fatalf("expected no error, got %s", err)
+		}
+	})
+}
diff --git a/tfexec/internal/e2etest/testdata/var/main.tf b/tfexec/internal/e2etest/testdata/var/main.tf
new file mode 100644
index 00000000..4abb28c3
--- /dev/null
+++ b/tfexec/internal/e2etest/testdata/var/main.tf
@@ -0,0 +1,6 @@
+variable "default" {
+  default = "foo"
+}
+
+variable "no_default" {
+} 
\ No newline at end of file
diff --git a/tfexec/internal/e2etest/util_test.go b/tfexec/internal/e2etest/util_test.go
index faf50454..0862b4a8 100644
--- a/tfexec/internal/e2etest/util_test.go
+++ b/tfexec/internal/e2etest/util_test.go
@@ -8,6 +8,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 
 	"github.com/hashicorp/go-version"
@@ -62,7 +63,7 @@ func runTestVersions(t *testing.T, versions []string, fixtureName string, cb fun
 				}
 			}
 
-			var stdouterr bytes.Buffer
+			var stdouterr strings.Builder
 			tf.SetStdout(&stdouterr)
 			tf.SetStderr(&stdouterr)