Index: clang-tidy/ClangTidyDiagnosticConsumer.cpp
===================================================================
--- clang-tidy/ClangTidyDiagnosticConsumer.cpp
+++ clang-tidy/ClangTidyDiagnosticConsumer.cpp
@@ -19,6 +19,8 @@
 #include "ClangTidyDiagnosticConsumer.h"
 #include "llvm/ADT/SmallString.h"
 
+#include <set>
+
 namespace clang {
 namespace tidy {
 
@@ -116,11 +118,31 @@
   }
 }
 
+struct LessClangTidyError {
+  bool operator()(const ClangTidyError *LHS, const ClangTidyError *RHS) const {
+    const ClangTidyMessage &M1 = LHS->Message;
+    const ClangTidyMessage &M2 = RHS->Message;
+
+    if (M1.FileOffset != M2.FileOffset)
+      return M1.FileOffset < M2.FileOffset;
+    int Result = M1.FilePath.compare(M2.FilePath);
+    if (Result != 0)
+      return Result < 0;
+    Result = M1.Message.compare(M2.Message);
+    if (Result != 0)
+      return Result < 0;
+    return false;
+  }
+};
+
 // Flushes the internal diagnostics buffer to the ClangTidyContext.
 void ClangTidyDiagnosticConsumer::finish() {
   finalizeLastError();
-  for (const ClangTidyError &Error : Errors)
-    Context.storeError(Error);
+  std::set<const ClangTidyError*, LessClangTidyError> UniqueErrors;
+  for (const ClangTidyError &Error : Errors) {
+    if (UniqueErrors.insert(&Error).second)
+      Context.storeError(Error);
+  }
   Errors.clear();
 }
 
Index: test/clang-tidy/deduplication.cpp
===================================================================
--- /dev/null
+++ test/clang-tidy/deduplication.cpp
@@ -0,0 +1,12 @@
+// RUN: clang-tidy -checks=google-explicit-constructor %s -- | FileCheck %s
+
+template<typename T>
+class A { A(T); };
+// CHECK: :[[@LINE-1]]:11: warning: Single-argument constructors must be explicit [google-explicit-constructor]
+// CHECK-NOT: warning:
+
+
+void f() {
+  A<int> a;
+  A<double> b;
+}