Index: clang-tidy/readability/RedundantDeclarationCheck.cpp
===================================================================
--- clang-tidy/readability/RedundantDeclarationCheck.cpp
+++ clang-tidy/readability/RedundantDeclarationCheck.cpp
@@ -19,7 +19,10 @@
 namespace readability {
 
 void RedundantDeclarationCheck::registerMatchers(MatchFinder *Finder) {
-  Finder->addMatcher(namedDecl(anyOf(varDecl(), functionDecl())).bind("Decl"),
+  auto UnlessDefinition = unless(isDefinition());
+  Finder->addMatcher(namedDecl(anyOf(varDecl(UnlessDefinition),
+                                     functionDecl(UnlessDefinition)))
+                         .bind("Decl"),
                      this);
 }
 
@@ -41,9 +44,6 @@
 
   bool MultiVar = false;
   if (const auto *VD = dyn_cast<VarDecl>(D)) {
-    if (VD->getPreviousDecl()->getStorageClass() == SC_Extern &&
-        VD->getStorageClass() != SC_Extern)
-      return;
     // Is this a multivariable declaration?
     for (const auto Other : VD->getDeclContext()->decls()) {
       if (Other != D && Other->getLocStart() == VD->getLocStart()) {
@@ -51,10 +51,6 @@
         break;
       }
     }
-  } else {
-    const auto *FD = cast<FunctionDecl>(D);
-    if (FD->isThisDeclarationADefinition())
-      return;
   }
 
   SourceLocation EndLoc = Lexer::getLocForEndOfToken(
Index: test/clang-tidy/readability-redundant-declaration.cpp
===================================================================
--- test/clang-tidy/readability-redundant-declaration.cpp
+++ test/clang-tidy/readability-redundant-declaration.cpp
@@ -24,7 +24,13 @@
 
 // Original check crashed for the code below.
 namespace std {
-  typedef decltype(sizeof(0)) size_t;
+typedef decltype(sizeof(0)) size_t;
 }
-void* operator new(std::size_t) __attribute__((__externally_visible__));
-void* operator new[](std::size_t) __attribute__((__externally_visible__));
+void *operator new(std::size_t) __attribute__((__externally_visible__));
+void *operator new[](std::size_t) __attribute__((__externally_visible__));
+
+// Don't warn about static member definition.
+struct C {
+  static int I;
+};
+int C::I;