diff --git a/src/netbase.h b/src/netbase.h
--- a/src/netbase.h
+++ b/src/netbase.h
@@ -38,7 +38,7 @@
     bool randomize_credentials;
 };
 
-enum Network ParseNetwork(std::string net);
+enum Network ParseNetwork(const std::string &net);
 std::string GetNetworkName(enum Network net);
 bool SetProxy(enum Network net, const proxyType &addrProxy);
 bool GetProxy(enum Network net, proxyType &proxyInfoOut);
diff --git a/src/netbase.cpp b/src/netbase.cpp
--- a/src/netbase.cpp
+++ b/src/netbase.cpp
@@ -33,8 +33,8 @@
 static const int SOCKS5_RECV_TIMEOUT = 20 * 1000;
 static std::atomic<bool> interruptSocks5Recv(false);
 
-enum Network ParseNetwork(std::string net) {
-    Downcase(net);
+enum Network ParseNetwork(const std::string &net_in) {
+    std::string net = ToLower(net_in);
     if (net == "ipv4") {
         return NET_IPV4;
     }
diff --git a/src/test/util_tests.cpp b/src/test/util_tests.cpp
--- a/src/test/util_tests.cpp
+++ b/src/test/util_tests.cpp
@@ -2031,17 +2031,9 @@
     BOOST_CHECK_EQUAL(ToLower(0), 0);
     BOOST_CHECK_EQUAL(ToLower('\xff'), '\xff');
 
-    std::string testVector;
-    Downcase(testVector);
-    BOOST_CHECK_EQUAL(testVector, "");
-
-    testVector = "#HODL";
-    Downcase(testVector);
-    BOOST_CHECK_EQUAL(testVector, "#hodl");
-
-    testVector = "\x00\xfe\xff";
-    Downcase(testVector);
-    BOOST_CHECK_EQUAL(testVector, "\x00\xfe\xff");
+    BOOST_CHECK_EQUAL(ToLower(""), "");
+    BOOST_CHECK_EQUAL(ToLower("#HODL"), "#hodl");
+    BOOST_CHECK_EQUAL(ToLower("\x00\xfe\xff"), "\x00\xfe\xff");
 }
 
 BOOST_AUTO_TEST_CASE(test_ToUpper) {
@@ -2051,6 +2043,10 @@
     BOOST_CHECK_EQUAL(ToUpper('{'), '{');
     BOOST_CHECK_EQUAL(ToUpper(0), 0);
     BOOST_CHECK_EQUAL(ToUpper('\xff'), '\xff');
+
+    BOOST_CHECK_EQUAL(ToUpper(""), "");
+    BOOST_CHECK_EQUAL(ToUpper("#hodl"), "#HODL");
+    BOOST_CHECK_EQUAL(ToUpper("\x00\xfe\xff"), "\x00\xfe\xff");
 }
 
 BOOST_AUTO_TEST_CASE(test_Capitalize) {
diff --git a/src/util/strencodings.h b/src/util/strencodings.h
--- a/src/util/strencodings.h
+++ b/src/util/strencodings.h
@@ -217,6 +217,8 @@
  * Converts the given character to its lowercase equivalent.
  * This function is locale independent. It only converts uppercase
  * characters in the standard 7-bit ASCII range.
+ * This is a feature, not a limitation.
+ *
  * @param[in] c     the character to convert to lowercase.
  * @return          the lowercase equivalent of c; or the argument
  *                  if no conversion is possible.
@@ -226,17 +228,22 @@
 }
 
 /**
- * Converts the given string to its lowercase equivalent.
+ * Returns the lowercase equivalent of the given string.
  * This function is locale independent. It only converts uppercase
  * characters in the standard 7-bit ASCII range.
- * @param[in,out] str   the string to convert to lowercase.
+ * This is a feature, not a limitation.
+ *
+ * @param[in] str   the string to convert to lowercase.
+ * @returns         lowercased equivalent of str
  */
-void Downcase(std::string &str);
+std::string ToLower(const std::string &str);
 
 /**
  * Converts the given character to its uppercase equivalent.
  * This function is locale independent. It only converts lowercase
  * characters in the standard 7-bit ASCII range.
+ * This is a feature, not a limitation.
+ *
  * @param[in] c     the character to convert to uppercase.
  * @return          the uppercase equivalent of c; or the argument
  *                  if no conversion is possible.
@@ -245,13 +252,25 @@
     return (c >= 'a' && c <= 'z' ? (c - 'a') + 'A' : c);
 }
 
+/**
+ * Returns the uppercase equivalent of the given string.
+ * This function is locale independent. It only converts lowercase
+ * characters in the standard 7-bit ASCII range.
+ * This is a feature, not a limitation.
+ *
+ * @param[in] str   the string to convert to uppercase.
+ * @returns         UPPERCASED EQUIVALENT OF str
+ */
+std::string ToUpper(const std::string &str);
+
 /**
  * Capitalizes the first character of the given string.
- * This function is locale independent. It only capitalizes the
- * first character of the argument if it has an uppercase equivalent
- * in the standard 7-bit ASCII range.
+ * This function is locale independent. It only converts lowercase
+ * characters in the standard 7-bit ASCII range.
+ * This is a feature, not a limitation.
+ *
  * @param[in] str   the string to capitalize.
- * @return          string with the first letter capitalized.
+ * @returns         string with the first letter capitalized.
  */
 std::string Capitalize(std::string str);
 
diff --git a/src/util/strencodings.cpp b/src/util/strencodings.cpp
--- a/src/util/strencodings.cpp
+++ b/src/util/strencodings.cpp
@@ -619,8 +619,20 @@
     return true;
 }
 
-void Downcase(std::string &str) {
-    std::transform(str.begin(), str.end(), str.begin(), ToLower);
+std::string ToLower(const std::string &str) {
+    std::string r;
+    for (auto ch : str) {
+        r += ToLower(ch);
+    }
+    return r;
+}
+
+std::string ToUpper(const std::string &str) {
+    std::string r;
+    for (auto ch : str) {
+        r += ToUpper(ch);
+    }
+    return r;
 }
 
 std::string Capitalize(std::string str) {
diff --git a/src/util/system.cpp b/src/util/system.cpp
--- a/src/util/system.cpp
+++ b/src/util/system.cpp
@@ -302,7 +302,7 @@
         key.erase(is_index);
     }
 #ifdef WIN32
-    std::transform(key.begin(), key.end(), key.begin(), ToLower);
+    key = ToLower(key);
     if (key[0] == '/') {
         key[0] = '-';
     }