diff --git a/taglib/toolkit/tstring.cpp b/taglib/toolkit/tstring.cpp
index 79b564fa..fa93c4cf 100644
--- a/taglib/toolkit/tstring.cpp
+++ b/taglib/toolkit/tstring.cpp
@@ -560,6 +560,8 @@ String &String::operator+=(wchar_t c)
 
 String &String::operator+=(char c)
 {
+  detach();
+
   d->data += uchar(c);
   return *this;
 }
diff --git a/tests/test_string.cpp b/tests/test_string.cpp
index b1b2c83d..c3b42ea4 100644
--- a/tests/test_string.cpp
+++ b/tests/test_string.cpp
@@ -37,6 +37,8 @@ class TestString : public CppUnit::TestFixture
   CPPUNIT_TEST(testUTF16Decode);
   CPPUNIT_TEST(testUTF16DecodeInvalidBOM);
   CPPUNIT_TEST(testUTF16DecodeEmptyWithBOM);
+  CPPUNIT_TEST(testAppendCharDetach);
+  CPPUNIT_TEST(testAppendStringDetach);
   CPPUNIT_TEST_SUITE_END();
 
 public:
@@ -131,6 +133,24 @@ public:
     CPPUNIT_ASSERT_EQUAL(String(), String(b, String::UTF16));
   }
 
+  void testAppendStringDetach()
+  {
+    String a("a");
+    String b = a;
+    a += "b";
+    CPPUNIT_ASSERT_EQUAL(String("ab"), a);
+    CPPUNIT_ASSERT_EQUAL(String("a"), b);
+  }
+
+  void testAppendCharDetach()
+  {
+    String a("a");
+    String b = a;
+    a += 'b';
+    CPPUNIT_ASSERT_EQUAL(String("ab"), a);
+    CPPUNIT_ASSERT_EQUAL(String("a"), b);
+  }
+
 };
 
 CPPUNIT_TEST_SUITE_REGISTRATION(TestString);