diff --git a/clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp b/clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp
--- a/clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp
@@ -183,9 +183,9 @@
         Param->hasAttr<UnusedAttr>())
       continue;
 
-    // In non-strict mode ignore function definitions with empty bodies
+    // In non-strict mode ignore public function definitions with empty bodies
     // (constructor initializer counts for non-empty body).
-    if (StrictMode ||
+    if (StrictMode || !Function->isExternallyVisible() ||
         (Function->getBody()->child_begin() !=
          Function->getBody()->child_end()) ||
         (isa<CXXConstructorDecl>(Function) &&
diff --git a/clang-tools-extra/docs/clang-tidy/checks/misc-unused-parameters.rst b/clang-tools-extra/docs/clang-tidy/checks/misc-unused-parameters.rst
--- a/clang-tools-extra/docs/clang-tidy/checks/misc-unused-parameters.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/misc-unused-parameters.rst
@@ -37,6 +37,8 @@
 
    When `false` (default value), the check will ignore trivially unused parameters,
    i.e. when the corresponding function has an empty body (and in case of
-   constructors - no constructor initializers). When the function body is empty,
-   an unused parameter is unlikely to be unnoticed by a human reader, and
-   there's basically no place for a bug to hide.
+   constructors - no constructor initializers) and the definition is public. When
+   the function body is empty, an unused parameter is unlikely to be unnoticed by
+   a human reader, and there's basically no place for a bug to hide. On the other
+   hand for non-public functions, all the call-sites are visible and the parameter
+   can be eliminated entirely.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/misc-unused-parameters.cpp b/clang-tools-extra/test/clang-tidy/checkers/misc-unused-parameters.cpp
--- a/clang-tools-extra/test/clang-tidy/checkers/misc-unused-parameters.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/misc-unused-parameters.cpp
@@ -154,6 +154,10 @@
 namespace {
 class C {
 public:
+// CHECK-FIXES: C() {}
+  C(int i) {}
+// CHECK-MESSAGES: :[[@LINE-1]]:9: warning
+
   void f(int i);
 // CHECK-FIXES: void f();
   void g(int i) {;}
@@ -181,7 +185,7 @@
 void useFunction(T t);
 
 void someMoreCallSites() {
-  C c;
+  C c(42);
   c.f(1);
 // CHECK-FIXES: c.f();
   c.g(1);