diff --git a/runtime/vm.go b/runtime/vm.go
index 34ff212..cc1990b 100644
--- a/runtime/vm.go
+++ b/runtime/vm.go
@@ -644,7 +644,7 @@ func (v *VM) Run() error {
 			case *objects.Array:
 				numElements := int64(len(left.Value))
 
-				if lowIdx < 0 || lowIdx >= numElements {
+				if lowIdx < 0 || lowIdx > numElements {
 					return fmt.Errorf("index out of bounds: %d", lowIdx)
 				}
 				if highIdx < 0 {
@@ -669,7 +669,7 @@ func (v *VM) Run() error {
 			case *objects.ImmutableArray:
 				numElements := int64(len(left.Value))
 
-				if lowIdx < 0 || lowIdx >= numElements {
+				if lowIdx < 0 || lowIdx > numElements {
 					return fmt.Errorf("index out of bounds: %d", lowIdx)
 				}
 				if highIdx < 0 {
@@ -694,7 +694,7 @@ func (v *VM) Run() error {
 			case *objects.String:
 				numElements := int64(len(left.Value))
 
-				if lowIdx < 0 || lowIdx >= numElements {
+				if lowIdx < 0 || lowIdx > numElements {
 					return fmt.Errorf("index out of bounds: %d", lowIdx)
 				}
 				if highIdx < 0 {
diff --git a/runtime/vm_string_test.go b/runtime/vm_string_test.go
index d3e7985..76611ff 100644
--- a/runtime/vm_string_test.go
+++ b/runtime/vm_string_test.go
@@ -28,7 +28,7 @@ func TestString(t *testing.T) {
 	expectError(t, fmt.Sprintf("%s[%d]", strStr, strLen))
 
 	// slice operator
-	for low := 0; low < strLen; low++ {
+	for low := 0; low <= strLen; low++ {
 		for high := low; high <= strLen; high++ {
 			expect(t, fmt.Sprintf("out = %s[%d:%d]", strStr, low, high), str[low:high])
 			expect(t, fmt.Sprintf("out = %s[0 + %d : 0 + %d]", strStr, low, high), str[low:high])