Index: clang-tidy/readability/RedundantDeclarationCheck.cpp
===================================================================
--- clang-tidy/readability/RedundantDeclarationCheck.cpp
+++ clang-tidy/readability/RedundantDeclarationCheck.cpp
@@ -30,6 +30,8 @@
     return;
   if (Prev->getLocation() == D->getLocation())
     return;
+  if (!Prev->getLocation().isValid())
+    return;
 
   const SourceManager &SM = *Result.SourceManager;
 
Index: test/clang-tidy/readability-redundant-declaration.cpp
===================================================================
--- test/clang-tidy/readability-redundant-declaration.cpp
+++ 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__));