diff --git a/Glob.cxx b/Glob.cxx
index e2af4ec36f..90970ea589 100644
--- a/Glob.cxx
+++ b/Glob.cxx
@@ -162,7 +162,7 @@ std::string Glob::PatternToRegex(std::string const& pattern,
         // On case-insensitive systems file names are converted to lower
         // case before matching.
         if (!preserve_case) {
-          ch = tolower(ch);
+          ch = tolower(static_cast<unsigned char>(ch));
         }
       }
 #endif
diff --git a/ProcessUNIX.c b/ProcessUNIX.c
index a918b8d9a7..01dc039822 100644
--- a/ProcessUNIX.c
+++ b/ProcessUNIX.c
@@ -2502,7 +2502,8 @@ static pid_t kwsysProcessFork(kwsysProcess* cp,
    corresponding parsing format string.  The parsing format should
    have two integers to store: the pid and then the ppid.  */
 #if defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__) ||       \
-  defined(__OpenBSD__) || defined(__GLIBC__) || defined(__GNU__)
+  defined(__NetBSD__) || defined(__OpenBSD__) || defined(__GLIBC__) ||        \
+  defined(__GNU__)
 #  define KWSYSPE_PS_COMMAND "ps axo pid,ppid"
 #  define KWSYSPE_PS_FORMAT "%d %d\n"
 #elif defined(__sun) && (defined(__SVR4) || defined(__svr4__)) /* Solaris */
diff --git a/SystemTools.cxx b/SystemTools.cxx
index f8205c795d..3f036df651 100644
--- a/SystemTools.cxx
+++ b/SystemTools.cxx
@@ -320,7 +320,8 @@ inline char const* Getcwd(char* buf, unsigned int len)
     if (nlen < len) {
       // make sure the drive letter is capital
       if (nlen > 1 && buf[1] == ':') {
-        buf[0] = toupper(buf[0]);
+        buf[0] =
+          static_cast<char>(toupper(static_cast<unsigned char>(buf[0])));
       }
       return buf;
     }
@@ -552,7 +553,8 @@ std::string SystemToolsStatic::GetCasePathName(std::string const& pathIn)
   casePath = path_components[idx++];
   // make sure drive letter is always upper case
   if (casePath.size() > 1 && casePath[1] == ':') {
-    casePath[0] = toupper(casePath[0]);
+    casePath[0] = static_cast<std::string::value_type>(
+      toupper(static_cast<unsigned char>(casePath[0])));
   }
   char const* sep = "";
 
@@ -1656,9 +1658,11 @@ std::string SystemTools::Capitalized(std::string const& s)
     return n;
   }
   n.resize(s.size());
-  n[0] = static_cast<std::string::value_type>(toupper(s[0]));
+  n[0] = static_cast<std::string::value_type>(
+    toupper(static_cast<unsigned char>(s[0])));
   for (size_t i = 1; i < s.size(); i++) {
-    n[i] = static_cast<std::string::value_type>(tolower(s[i]));
+    n[i] = static_cast<std::string::value_type>(
+      tolower(static_cast<unsigned char>(s[i])));
   }
   return n;
 }
@@ -1677,7 +1681,8 @@ std::string SystemTools::CapitalizedWords(std::string const& s)
     if (isalpha(s[i]) && (i == 0 || isspace(s[i - 1])))
 #endif
     {
-      n[i] = static_cast<std::string::value_type>(toupper(s[i]));
+      n[i] = static_cast<std::string::value_type>(
+        toupper(static_cast<unsigned char>(s[i])));
     }
   }
   return n;
@@ -1697,7 +1702,8 @@ std::string SystemTools::UnCapitalizedWords(std::string const& s)
     if (isalpha(s[i]) && (i == 0 || isspace(s[i - 1])))
 #endif
     {
-      n[i] = static_cast<std::string::value_type>(tolower(s[i]));
+      n[i] = static_cast<std::string::value_type>(
+        tolower(static_cast<unsigned char>(s[i])));
     }
   }
   return n;
@@ -1768,7 +1774,8 @@ std::string SystemTools::LowerCase(std::string const& s)
   std::string n;
   n.resize(s.size());
   for (size_t i = 0; i < s.size(); i++) {
-    n[i] = static_cast<std::string::value_type>(tolower(s[i]));
+    n[i] = static_cast<std::string::value_type>(
+      tolower(static_cast<unsigned char>(s[i])));
   }
   return n;
 }
@@ -1779,7 +1786,8 @@ std::string SystemTools::UpperCase(std::string const& s)
   std::string n;
   n.resize(s.size());
   for (size_t i = 0; i < s.size(); i++) {
-    n[i] = static_cast<std::string::value_type>(toupper(s[i]));
+    n[i] = static_cast<std::string::value_type>(
+      toupper(static_cast<unsigned char>(s[i])));
   }
   return n;
 }
@@ -2743,8 +2751,8 @@ int SystemTools::Strucmp(char const* l, char const* r)
   int lc;
   int rc;
   do {
-    lc = tolower(*l++);
-    rc = tolower(*r++);
+    lc = tolower(static_cast<unsigned char>(*l++));
+    rc = tolower(static_cast<unsigned char>(*r++));
   } while (lc == rc && lc);
   return lc - rc;
 }
diff --git a/testSystemTools.cxx b/testSystemTools.cxx
index dff9dd6224..b94b8f6f1b 100644
--- a/testSystemTools.cxx
+++ b/testSystemTools.cxx
@@ -534,6 +534,21 @@ static bool CheckStringOperations()
 {
   bool res = true;
 
+  // Case conversion should only affect ASCII bytes.
+  // Test using a UTF-8 Copyright Symbol because its leading byte
+  // is transformed by MSVC's tolower in a US-ASCII locale.
+  static std::string const sampleUTF8 = "y\xC2\xA9Z"; // Copyright Symbol
+  if (kwsys::SystemTools::LowerCase(sampleUTF8) != "y\xC2\xA9z") {
+    std::cerr << "Problem with LowerCase " << '"' << sampleUTF8 << '"'
+              << std::endl;
+    res = false;
+  }
+  if (kwsys::SystemTools::UpperCase(sampleUTF8) != "Y\xC2\xA9Z") {
+    std::cerr << "Problem with UpperCase " << '"' << sampleUTF8 << '"'
+              << std::endl;
+    res = false;
+  }
+
   std::string test = "mary had a little lamb.";
   if (kwsys::SystemTools::CapitalizedWords(test) !=
       "Mary Had A Little Lamb.") {