diff --git a/interpreter/interpreter.go b/interpreter/interpreter.go
index 9aaf7f0..7bc62e8 100644
--- a/interpreter/interpreter.go
+++ b/interpreter/interpreter.go
@@ -111,7 +111,7 @@ func (s *programState) parseVars(varDeclrs []parser.VarDeclaration, rawVars map[
 		if varsDecl.Origin == nil {
 			raw, ok := rawVars[varsDecl.Name.Name]
 			if !ok {
-				panic("TODO handle var not found: " + varsDecl.Name.Name)
+				return MissingVariableErr{Name: varsDecl.Name.Name}
 			}
 			parsed, err := parseVar(varsDecl.Type.Name, raw)
 			if err != nil {
@@ -200,7 +200,7 @@ func (st *programState) evaluateLit(literal parser.Literal) (Value, error) {
 	case *parser.VariableLiteral:
 		value, ok := st.Vars[literal.Name]
 		if !ok {
-			panic("TODO err for unbound variable")
+			return nil, UnboundVariableErr{Name: literal.Name}
 		}
 		return value, nil
 	default:
diff --git a/interpreter/interpreter_error.go b/interpreter/interpreter_error.go
index a8a9c4c..e7cb793 100644
--- a/interpreter/interpreter_error.go
+++ b/interpreter/interpreter_error.go
@@ -22,3 +22,19 @@ type TypeError struct {
 func (e TypeError) Error() string {
 	return fmt.Sprintf("Invalid value received. Expecting value of type %s (got %s instead)", e.Expected, e.Value.String())
 }
+
+type UnboundVariableErr struct {
+	Name string
+}
+
+func (e UnboundVariableErr) Error() string {
+	return fmt.Sprintf("Unbound variable: %s", e.Name)
+}
+
+type MissingVariableErr struct {
+	Name string
+}
+
+func (e MissingVariableErr) Error() string {
+	return fmt.Sprintf("Variable is missing in json: %s", e.Name)
+}
diff --git a/interpreter/interpreter_test.go b/interpreter/interpreter_test.go
index a3016e9..80ac03d 100644
--- a/interpreter/interpreter_test.go
+++ b/interpreter/interpreter_test.go
@@ -1383,4 +1383,39 @@ func TestErrors(t *testing.T) {
 		test(t, tc)
 	})
 
+	t.Run("unbound variable", func(t *testing.T) {
+		tc := NewTestCase()
+		tc.compile(t, `
+	send $unbound_var (
+		source = @a
+		destination = @b
+	)`)
+
+		tc.expected = CaseResult{
+			Error: machine.UnboundVariableErr{
+				Name: "unbound_var",
+			},
+		}
+		test(t, tc)
+	})
+
+	t.Run("missing variable from json", func(t *testing.T) {
+		tc := NewTestCase()
+		tc.compile(t, `
+	vars {
+		monetary $x
+	}
+
+	send $x (
+		source = @a
+		destination = @b
+	)`)
+
+		tc.expected = CaseResult{
+			Error: machine.MissingVariableErr{
+				Name: "x",
+			},
+		}
+		test(t, tc)
+	})
 }