diff --git a/string.c b/string.c
index a526d9b712..49e3c18152 100644
--- a/string.c
+++ b/string.c
@@ -3709,7 +3709,7 @@ rb_str_splice_0(VALUE str, long beg, long len, VALUE val)
     RSTRING_GETMEM(str, sptr, slen);
     if (len < vlen) {
 	/* expand string */
-	RESIZE_CAPA(str, slen + vlen - len + TERM_LEN(str));
+	RESIZE_CAPA(str, slen + vlen - len);
 	sptr = RSTRING_PTR(str);
     }
 
@@ -3726,7 +3726,7 @@ rb_str_splice_0(VALUE str, long beg, long len, VALUE val)
     }
     slen += vlen - len;
     STR_SET_LEN(str, slen);
-    sptr[slen] = '\0';
+    TERM_FILL(&sptr[slen], TERM_LEN(str));
     OBJ_INFECT(str, val);
 }
 
diff --git a/test/-ext-/string/test_cstr.rb b/test/-ext-/string/test_cstr.rb
index 89ab3bb7b0..a7cb0ebe9c 100644
--- a/test/-ext-/string/test_cstr.rb
+++ b/test/-ext-/string/test_cstr.rb
@@ -56,6 +56,10 @@ class Test_StringCStr < Test::Unit::TestCase
     assert_wchars_term_char("a\n") {|s| s.chomp!}
   end
 
+  def test_wchar_aset
+    assert_wchars_term_char("a"*30) {|s| s[29,1] = ""}
+  end
+
   def assert_wchars_term_char(str)
     result = {}
     WCHARS.map do |enc|