diff --git a/error.c b/error.c
index 039999cf6a..98b8c7801a 100644
--- a/error.c
+++ b/error.c
@@ -1415,8 +1415,8 @@ frozen_err_initialize(int argc, VALUE *argv, VALUE self)
 
     argc = rb_scan_args(argc, argv, "02", &mesg, &recv);
     if (argc > 1) {
-	argc--;
-	rb_ivar_set(self, id_recv, recv);
+        argc--;
+        rb_ivar_set(self, id_recv, recv);
     }
     rb_call_super(argc, argv);
     return self;
@@ -2897,13 +2897,13 @@ rb_error_frozen_object(VALUE frozen_obj)
 	VALUE path = rb_ary_entry(debug_info, 0);
 	VALUE line = rb_ary_entry(debug_info, 1);
 
-	rb_frozen_error_raise(frozen_obj,
-	    "can't modify frozen %"PRIsVALUE", created at %"PRIsVALUE":%"PRIsVALUE,
-	    CLASS_OF(frozen_obj), path, line);
+        rb_frozen_error_raise(frozen_obj,
+            "can't modify frozen %"PRIsVALUE", created at %"PRIsVALUE":%"PRIsVALUE,
+            CLASS_OF(frozen_obj), path, line);
     }
     else {
-	rb_frozen_error_raise(frozen_obj, "can't modify frozen %"PRIsVALUE,
-	    CLASS_OF(frozen_obj));
+        rb_frozen_error_raise(frozen_obj, "can't modify frozen %"PRIsVALUE,
+            CLASS_OF(frozen_obj));
     }
 }
 
diff --git a/eval.c b/eval.c
index e778d074dd..b9643803d5 100644
--- a/eval.c
+++ b/eval.c
@@ -454,7 +454,7 @@ rb_class_modify_check(VALUE klass)
 		goto noclass;
 	    }
 	}
-	rb_frozen_error_raise(klass, "can't modify frozen %s", desc);
+        rb_frozen_error_raise(klass, "can't modify frozen %s", desc);
     }
 }
 
diff --git a/thread.c b/thread.c
index d4f33a2e42..bfe741c908 100644
--- a/thread.c
+++ b/thread.c
@@ -3325,7 +3325,7 @@ VALUE
 rb_thread_local_aset(VALUE thread, ID id, VALUE val)
 {
     if (OBJ_FROZEN(thread)) {
-	rb_frozen_error_raise(thread, "can't modify frozen thread locals");
+        rb_frozen_error_raise(thread, "can't modify frozen thread locals");
     }
 
     return threadptr_local_aset(rb_thread_ptr(thread), id, val);
@@ -3402,7 +3402,7 @@ rb_thread_variable_set(VALUE thread, VALUE id, VALUE val)
     VALUE locals;
 
     if (OBJ_FROZEN(thread)) {
-	rb_frozen_error_raise(thread, "can't modify frozen thread locals");
+        rb_frozen_error_raise(thread, "can't modify frozen thread locals");
     }
 
     locals = rb_ivar_get(thread, id_locals);