diff --git a/clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.cpp b/clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.cpp
--- a/clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.cpp
+++ b/clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.cpp
@@ -8,6 +8,7 @@
 
 #include "RenamerClangTidyCheck.h"
 #include "ASTUtils.h"
+#include "clang/AST/ASTFwd.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/Frontend/CompilerInstance.h"
@@ -272,6 +273,13 @@
   }
 
   if (const auto *Decl = Result.Nodes.getNodeAs<NamedDecl>("decl")) {
+
+    // fix using namespace decls
+    if (const auto *UsingNS = dyn_cast<UsingDirectiveDecl>(Decl)) {
+      addUsage(NamingCheckFailures, UsingNS->getNominatedNamespaceAsWritten(),
+               UsingNS->getIdentLocation());
+    }
+
     if (!Decl->getIdentifier() || Decl->getName().empty() || Decl->isImplicit())
       return;
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/readability-identifier-naming.cpp b/clang-tools-extra/test/clang-tidy/checkers/readability-identifier-naming.cpp
--- a/clang-tools-extra/test/clang-tidy/checkers/readability-identifier-naming.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/readability-identifier-naming.cpp
@@ -527,3 +527,8 @@
 // CHECK-FIXES: {{^}}    int * const lc_PointerB = nullptr;{{$}}
 }
 
+using namespace FOO_NS;
+// CHECK-FIXES: {{^}}using namespace foo_ns;
+
+using namespace FOO_NS::InlineNamespace;
+// CHECK-FIXES: {{^}}using namespace foo_ns::inline_namespace;