Index: cfe/trunk/lib/Tooling/InterpolatingCompilationDatabase.cpp
===================================================================
--- cfe/trunk/lib/Tooling/InterpolatingCompilationDatabase.cpp
+++ cfe/trunk/lib/Tooling/InterpolatingCompilationDatabase.cpp
@@ -191,9 +191,9 @@
     // --std flag may only be transferred if the language is the same.
     // We may consider "translating" these, e.g. c++11 -> c11.
     if (Std != LangStandard::lang_unspecified && foldType(TargetType) == Type) {
-      Result.CommandLine.push_back("-std");
       Result.CommandLine.push_back(
-          LangStandard::getLangStandardForKind(Std).getName());
+          "-std=" +
+          std::string(LangStandard::getLangStandardForKind(Std).getName()));
     }
     Result.CommandLine.push_back(Filename);
     return Result;
Index: cfe/trunk/unittests/Tooling/CompilationDatabaseTest.cpp
===================================================================
--- cfe/trunk/unittests/Tooling/CompilationDatabaseTest.cpp
+++ cfe/trunk/unittests/Tooling/CompilationDatabaseTest.cpp
@@ -711,9 +711,9 @@
 
   // .h is ambiguous, so we add explicit language flags
   EXPECT_EQ(getCommand("foo.h"),
-            "clang -D dir/foo.cpp -x c++-header -std c++17");
+            "clang -D dir/foo.cpp -x c++-header -std=c++17");
   // and don't add -x if the inferred language is correct.
-  EXPECT_EQ(getCommand("foo.hpp"), "clang -D dir/foo.cpp -std c++17");
+  EXPECT_EQ(getCommand("foo.hpp"), "clang -D dir/foo.cpp -std=c++17");
   // respect -x if it's already there.
   EXPECT_EQ(getCommand("baz.h"), "clang -D dir/baz.cee -x c-header");
   // prefer a worse match with the right language