Index: clang-tools-extra/pp-trace/PPCallbacksTracker.h
===================================================================
--- clang-tools-extra/pp-trace/PPCallbacksTracker.h
+++ clang-tools-extra/pp-trace/PPCallbacksTracker.h
@@ -135,6 +135,7 @@
                              StringRef Str) override;
   void PragmaExecCharsetPop(PragmaIntroducer Introducer,
                             SourceLocation Loc) override;
+  void PragmaOnce(PragmaIntroducer Introducer, SourceLocation Loc) override;
   void MacroExpands(const Token &MacroNameTok, const MacroDefinition &MD,
                     SourceRange Range, const MacroArgs *Args) override;
   void MacroDefined(SourceLocation HashLoc, const Token &MacroNameTok,
Index: clang-tools-extra/pp-trace/PPCallbacksTracker.cpp
===================================================================
--- clang-tools-extra/pp-trace/PPCallbacksTracker.cpp
+++ clang-tools-extra/pp-trace/PPCallbacksTracker.cpp
@@ -337,6 +337,14 @@
   appendArgument("Loc", Loc);
 }
 
+/// Callback invoked when a \#pragma once directive is read.
+void PPCallbacksTracker::PragmaOnce(PragmaIntroducer Introducer,
+                                    SourceLocation Loc) {
+  beginCallback("PragmaOnce");
+  appendArgument("Introducer", Introducer);
+  appendArgument("Loc", Loc);
+}
+
 // Called by Preprocessor::HandleMacroExpandedIdentifier when a
 // macro invocation is found.
 void PPCallbacksTracker::MacroExpands(const Token &MacroNameTok,
Index: clang-tools-extra/test/pp-trace/pp-trace-pragma-general.cpp
===================================================================
--- clang-tools-extra/test/pp-trace/pp-trace-pragma-general.cpp
+++ clang-tools-extra/test/pp-trace/pp-trace-pragma-general.cpp
@@ -1,4 +1,4 @@
-// RUN: pp-trace -callbacks '*,-FileChanged,-MacroDefined' %s -- | FileCheck --strict-whitespace %s
+// RUN: pp-trace -callbacks '*,-FileChanged,-MacroDefined' -extra-arg-before=-xc++-header %s -- | FileCheck --strict-whitespace %s
 
 #pragma clang diagnostic push
 #pragma clang diagnostic pop
@@ -19,6 +19,8 @@
 { }
 }
 
+#pragma once
+
 // CHECK: ---
 // CHECK-NEXT: - Callback: PragmaDirective
 // CHECK-NEXT:   Introducer: {Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:3:1", Kind: PIK_HashPragma}
@@ -114,5 +116,10 @@
 // CHECK-NEXT:   Introducer: {Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:18:1", Kind: PIK_HashPragma}
 // CHECK-NEXT:   Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:18:23"
 // CHECK-NEXT:   DebugType: captured
+// CHECK-NEXT: - Callback: PragmaDirective
+// CHECK-NEXT:   Introducer: {Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:22:1", Kind: PIK_HashPragma}
+// CHECK-NEXT: - Callback: PragmaOnce
+// CHECK-NEXT:   Introducer: {Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:22:1", Kind: PIK_HashPragma}
+// CHECK-NEXT:   Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:22:9"
 // CHECK-NEXT: - Callback: EndOfMainFile
 // CHECK-NEXT: ...