Index: clang/include/clang/Lex/DependencyDirectivesSourceMinimizer.h
===================================================================
--- clang/include/clang/Lex/DependencyDirectivesSourceMinimizer.h
+++ clang/include/clang/Lex/DependencyDirectivesSourceMinimizer.h
@@ -38,6 +38,7 @@
   pp_undef,
   pp_import,
   pp_pragma_import,
+  pp_pragma_once,
   pp_include_next,
   pp_if,
   pp_ifdef,
Index: clang/lib/Lex/DependencyDirectivesSourceMinimizer.cpp
===================================================================
--- clang/lib/Lex/DependencyDirectivesSourceMinimizer.cpp
+++ clang/lib/Lex/DependencyDirectivesSourceMinimizer.cpp
@@ -612,7 +612,21 @@
 
 bool Minimizer::lexPragma(const char *&First, const char *const End) {
   // #pragma.
-  if (!isNextIdentifier("clang", First, End)) {
+  skipWhitespace(First, End);
+  if (First == End || !isIdentifierHead(*First))
+    return false;
+
+  IdInfo FoundId = lexIdentifier(First, End);
+  First = FoundId.Last;
+  if (FoundId.Name == "once") {
+    // #pragma once
+    skipLine(First, End);
+    makeToken(pp_pragma_once);
+    append("#pragma once\n");
+    return false;
+  }
+
+  if (FoundId.Name != "clang") {
     skipLine(First, End);
     return false;
   }
Index: clang/unittests/Lex/DependencyDirectivesSourceMinimizerTest.cpp
===================================================================
--- clang/unittests/Lex/DependencyDirectivesSourceMinimizerTest.cpp
+++ clang/unittests/Lex/DependencyDirectivesSourceMinimizerTest.cpp
@@ -544,4 +544,20 @@
   EXPECT_STREQ("#include <test.h>\n", Out.data());
 }
 
+TEST(MinimizeSourceToDependencyDirectivesTest, PragmaOnce) {
+  SmallVector<char, 128> Out;
+  SmallVector<Token, 4> Tokens;
+
+  StringRef Source = R"(// comment
+#pragma once
+// another comment
+#include <test.h>
+)";
+  ASSERT_FALSE(minimizeSourceToDependencyDirectives(Source, Out, Tokens));
+  EXPECT_STREQ("#pragma once\n#include <test.h>\n", Out.data());
+  ASSERT_EQ(Tokens.size(), 3u);
+  EXPECT_EQ(Tokens[0].K,
+            minimize_source_to_dependency_directives::pp_pragma_once);
+}
+
 } // end anonymous namespace