diff --git a/clang-tools-extra/clang-tidy/misc/UnusedUsingDeclsCheck.cpp b/clang-tools-extra/clang-tidy/misc/UnusedUsingDeclsCheck.cpp
--- a/clang-tools-extra/clang-tidy/misc/UnusedUsingDeclsCheck.cpp
+++ b/clang-tools-extra/clang-tidy/misc/UnusedUsingDeclsCheck.cpp
@@ -54,6 +54,7 @@
   Finder->addMatcher(loc(templateSpecializationType(forEachTemplateArgument(
                          templateArgument().bind("used")))),
                      this);
+  Finder->addMatcher(userDefinedLiteral().bind("used"), this);
   // Cases where we can identify the UsingShadowDecl directly, rather than
   // just its target.
   // FIXME: cover more cases in this way, as the AST supports it.
@@ -150,7 +151,11 @@
       if (const auto *USD = dyn_cast<UsingShadowDecl>(ND))
         removeFromFoundDecls(USD->getTargetDecl()->getCanonicalDecl());
     }
+    return;
   }
+  // Check user-defined literals
+  if (const auto *UDL = Result.Nodes.getNodeAs<UserDefinedLiteral>("used"))
+    removeFromFoundDecls(UDL->getCalleeDecl());
 }
 
 void UnusedUsingDeclsCheck::removeFromFoundDecls(const Decl *D) {
diff --git a/clang-tools-extra/test/clang-tidy/checkers/misc/unused-using-decls.cpp b/clang-tools-extra/test/clang-tidy/checkers/misc/unused-using-decls.cpp
--- a/clang-tools-extra/test/clang-tidy/checkers/misc/unused-using-decls.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/misc/unused-using-decls.cpp
@@ -48,6 +48,7 @@
 void OverloadFunc(int);
 void OverloadFunc(double);
 int FuncUsedByUsingDeclInMacro() { return 1; }
+long double operator""_w(long double);
 
 class ostream {
 public:
@@ -106,6 +107,7 @@
 using n::UnusedFunc; // UnusedFunc
 // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: using decl 'UnusedFunc' is unused
 // CHECK-FIXES: {{^}}// UnusedFunc
+using n::operator""_w;
 using n::cout;
 using n::endl;
 
@@ -183,6 +185,7 @@
   UsedInstance.i;
   UsedFunc();
   UsedTemplateFunc<int>();
+  1.5_w;
   cout << endl;
   Color2 color2;
   int t1 = Color3::Yellow;