Index: clang-tools-extra/trunk/clang-tidy/readability/RedundantDeclarationCheck.cpp
===================================================================
--- clang-tools-extra/trunk/clang-tidy/readability/RedundantDeclarationCheck.cpp
+++ clang-tools-extra/trunk/clang-tidy/readability/RedundantDeclarationCheck.cpp
@@ -28,6 +28,8 @@
   const auto *Prev = D->getPreviousDecl();
   if (!Prev)
     return;
+  if (!Prev->getLocation().isValid())
+    return;
   if (Prev->getLocation() == D->getLocation())
     return;
 
Index: clang-tools-extra/trunk/test/clang-tidy/readability-redundant-declaration.cpp
===================================================================
--- clang-tools-extra/trunk/test/clang-tidy/readability-redundant-declaration.cpp
+++ clang-tools-extra/trunk/test/clang-tidy/readability-redundant-declaration.cpp
@@ -21,3 +21,10 @@
 // CHECK-MESSAGES: :[[@LINE-1]]:12: warning: redundant 'f' declaration
 // CHECK-FIXES: {{^}}{{$}}
 static int f() {}
+
+// Original check crashed for the code below.
+namespace std {
+  typedef long unsigned int size_t;
+}
+void* operator new(std::size_t) __attribute__((__externally_visible__));
+void* operator new[](std::size_t) __attribute__((__externally_visible__));