diff --git a/helper/variables/flag.go b/helper/variables/flag.go
index 393586234..497b6fb1e 100644
--- a/helper/variables/flag.go
+++ b/helper/variables/flag.go
@@ -21,11 +21,18 @@ func (v *Flag) Set(raw string) error {
 	}
 
 	key, input := raw[0:idx], raw[idx+1:]
+	if key == "" {
+		return fmt.Errorf("No key to left '=' in arg: %s", raw)
+	}
+
 	value, err := ParseInput(input)
 	if err != nil {
 		return err
 	}
 
+	// Trim the whitespace on the key
+	key = strings.TrimSpace(key)
+
 	*v = Merge(*v, map[string]interface{}{key: value})
 	return nil
 }
diff --git a/helper/variables/flag_test.go b/helper/variables/flag_test.go
index f88b42cd1..66c8d1a65 100644
--- a/helper/variables/flag_test.go
+++ b/helper/variables/flag_test.go
@@ -19,6 +19,12 @@ func TestFlag(t *testing.T) {
 		Output map[string]interface{}
 		Error  bool
 	}{
+		{
+			"=value",
+			nil,
+			true,
+		},
+
 		{
 			"key=value",
 			map[string]interface{}{"key": "value"},
@@ -43,6 +49,24 @@ func TestFlag(t *testing.T) {
 			false,
 		},
 
+		{
+			"key =value",
+			map[string]interface{}{"key": "value"},
+			false,
+		},
+
+		{
+			"key = value",
+			map[string]interface{}{"key": " value"},
+			false,
+		},
+
+		{
+			`key = "value"`,
+			map[string]interface{}{"key": "value"},
+			false,
+		},
+
 		{
 			"map.key=foo",
 			map[string]interface{}{"map.key": "foo"},