diff --git a/taglib/ape/apetag.cpp b/taglib/ape/apetag.cpp
index 92ad536f..79e1d5cc 100644
--- a/taglib/ape/apetag.cpp
+++ b/taglib/ape/apetag.cpp
@@ -62,8 +62,9 @@ namespace
         return false;
     }
 
+    const String upperKey = String(key).upper();
     for(size_t i = 0; invalidKeys[i] != 0; ++i) {
-      if(String(key).upper() == invalidKeys[i])
+      if(upperKey == invalidKeys[i])
         return false;
     }
 
diff --git a/taglib/mpeg/id3v2/frames/unsynchronizedlyricsframe.cpp b/taglib/mpeg/id3v2/frames/unsynchronizedlyricsframe.cpp
index 87317d32..eafae171 100644
--- a/taglib/mpeg/id3v2/frames/unsynchronizedlyricsframe.cpp
+++ b/taglib/mpeg/id3v2/frames/unsynchronizedlyricsframe.cpp
@@ -118,7 +118,7 @@ PropertyMap UnsynchronizedLyricsFrame::asProperties() const
 {
   PropertyMap map;
   String key = description().upper();
-  if(key.isEmpty() || key.upper() == "LYRICS")
+  if(key.isEmpty() || key == "LYRICS")
     map.insert("LYRICS", text());
   else
     map.insert("LYRICS:" + key, text());
diff --git a/taglib/mpeg/id3v2/frames/urllinkframe.cpp b/taglib/mpeg/id3v2/frames/urllinkframe.cpp
index 99e4fb7f..543b5184 100644
--- a/taglib/mpeg/id3v2/frames/urllinkframe.cpp
+++ b/taglib/mpeg/id3v2/frames/urllinkframe.cpp
@@ -170,7 +170,7 @@ PropertyMap UserUrlLinkFrame::asProperties() const
 {
   PropertyMap map;
   String key = description().upper();
-  if(key.isEmpty() || key.upper() == "URL")
+  if(key.isEmpty() || key == "URL")
     map.insert("URL", url());
   else
     map.insert("URL:" + key, url());
diff --git a/taglib/toolkit/tstring.cpp b/taglib/toolkit/tstring.cpp
index bee4fb7e..863bbf59 100644
--- a/taglib/toolkit/tstring.cpp
+++ b/taglib/toolkit/tstring.cpp
@@ -469,12 +469,11 @@ String & String::clear()
 String String::upper() const
 {
   String s;
-
-  static int shift = 'A' - 'a';
+  s.d->data.reserve(size());
 
   for(ConstIterator it = begin(); it != end(); ++it) {
     if(*it >= 'a' && *it <= 'z')
-      s.d->data.push_back(*it + shift);
+      s.d->data.push_back(*it + 'A' - 'a');
     else
       s.d->data.push_back(*it);
   }