diff --git a/include/tscpp/util/TsSharedMutex.h b/include/tscpp/util/TsSharedMutex.h
index fa00fc67cba..3ac7f2ea948 100644
--- a/include/tscpp/util/TsSharedMutex.h
+++ b/include/tscpp/util/TsSharedMutex.h
@@ -59,12 +59,19 @@ class Strerror
 public:
   Strerror(int err_num)
   {
-    _c_str = strerror_r(err_num, _buf, 256);
-    if (!_c_str) {
+    // Handle either GNU or XSI version of strerror_r().
+    //
+    if (!_success(strerror_r(err_num, _buf, 256))) {
       _c_str = "strerror_r() call failed";
     } else {
       _buf[255] = '\0';
+      _c_str    = _buf;
     }
+
+    // Make sure there are no unused function warnings.
+    //
+    static_cast<void>(_success(0));
+    static_cast<void>(_success(nullptr));
   }
 
   char const *
@@ -76,6 +83,18 @@ class Strerror
 private:
   char _buf[256];
   char const *_c_str;
+
+  bool
+  _success(int retval)
+  {
+    return retval == 0;
+  }
+
+  bool
+  _success(char *retval)
+  {
+    return retval != nullptr;
+  }
 };
 
 // A class with the same interface as std::shared_mutex, but which is not prone to writer starvation.
@@ -200,7 +219,7 @@ class shared_mutex
 #endif
 #endif
 
-  void
+  static void
   _call_fatal(char const *func_name, void *ptr, int errnum)
   {
     TSFatal("%s(%p) failed: %s (%d)", func_name, ptr, Strerror(errnum).c_str(), errnum);