diff --git a/clang-tools-extra/clang-tidy/readability/RedundantDeclarationCheck.cpp b/clang-tools-extra/clang-tidy/readability/RedundantDeclarationCheck.cpp
--- a/clang-tools-extra/clang-tidy/readability/RedundantDeclarationCheck.cpp
+++ b/clang-tools-extra/clang-tidy/readability/RedundantDeclarationCheck.cpp
@@ -35,7 +35,8 @@
                       functionDecl(unless(anyOf(
                           isDefinition(), isDefaulted(),
                           doesDeclarationForceExternallyVisibleDefinition(),
-                          hasAncestor(friendDecl()))))))
+                          hasAncestor(friendDecl()))))),
+                optionally(hasParent(linkageSpecDecl().bind("extern"))))
           .bind("Decl"),
       this);
 }
@@ -78,9 +79,17 @@
       D->getSourceRange().getEnd(), 0, SM, Result.Context->getLangOpts());
   {
     auto Diag = diag(D->getLocation(), "redundant %0 declaration") << D;
-    if (!MultiVar && !DifferentHeaders)
-      Diag << FixItHint::CreateRemoval(
-          SourceRange(D->getSourceRange().getBegin(), EndLoc));
+    if (!MultiVar && !DifferentHeaders) {
+      SourceLocation BeginLoc;
+      if (const auto *Extern =
+              Result.Nodes.getNodeAs<LinkageSpecDecl>("extern");
+          Extern && !Extern->hasBraces())
+        BeginLoc = Extern->getExternLoc();
+      else
+        BeginLoc = D->getSourceRange().getBegin();
+
+      Diag << FixItHint::CreateRemoval(SourceRange(BeginLoc, EndLoc));
+    }
   }
   diag(Prev->getLocation(), "previously declared here", DiagnosticIDs::Note);
 }
diff --git a/clang-tools-extra/test/clang-tidy/checkers/readability/redundant-declaration.cpp b/clang-tools-extra/test/clang-tidy/checkers/readability/redundant-declaration.cpp
--- a/clang-tools-extra/test/clang-tidy/checkers/readability/redundant-declaration.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/readability/redundant-declaration.cpp
@@ -120,3 +120,9 @@
 // CHECK-MESSAGES-NOMSCOMPAT: :[[@LINE-1]]:20: warning: redundant 'g' declaration
 // CHECK-FIXES-NOMSCOMPAT: {{^}}// extern g{{$}}
 #endif
+
+// PR42068
+extern "C" int externX;
+int dumyBegin;extern "C" int externX;int dummyEnd;
+// CHECK-MESSAGES: :[[@LINE-1]]:30: warning: redundant 'externX' declaration [readability-redundant-declaration]
+// CHECK-FIXES: {{^}}int dumyBegin;int dummyEnd;{{$}}