diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
--- a/clang/include/clang/AST/Decl.h
+++ b/clang/include/clang/AST/Decl.h
@@ -78,33 +78,6 @@
 class UnresolvedSetImpl;
 class VarTemplateDecl;
 
-/// A container of type source information.
-///
-/// A client can read the relevant info using TypeLoc wrappers, e.g:
-/// @code
-/// TypeLoc TL = TypeSourceInfo->getTypeLoc();
-/// TL.getBeginLoc().print(OS, SrcMgr);
-/// @endcode
-class alignas(8) TypeSourceInfo {
-  // Contains a memory block after the class, used for type source information,
-  // allocated by ASTContext.
-  friend class ASTContext;
-
-  QualType Ty;
-
-  TypeSourceInfo(QualType ty) : Ty(ty) {}
-
-public:
-  /// Return the type wrapped by this type source info.
-  QualType getType() const { return Ty; }
-
-  /// Return the TypeLoc wrapper for the type source info.
-  TypeLoc getTypeLoc() const; // implemented in TypeLoc.h
-
-  /// Override the type stored in this TypeSourceInfo. Use with caution!
-  void overrideType(QualType T) { Ty = T; }
-};
-
 /// The top declaration context.
 class TranslationUnitDecl : public Decl, public DeclContext {
   ASTContext &Ctx;
diff --git a/clang/include/clang/AST/Type.h b/clang/include/clang/AST/Type.h
--- a/clang/include/clang/AST/Type.h
+++ b/clang/include/clang/AST/Type.h
@@ -6179,6 +6179,33 @@
   QualType apply(const ASTContext &Context, const Type* T) const;
 };
 
+/// A container of type source information.
+///
+/// A client can read the relevant info using TypeLoc wrappers, e.g:
+/// @code
+/// TypeLoc TL = TypeSourceInfo->getTypeLoc();
+/// TL.getBeginLoc().print(OS, SrcMgr);
+/// @endcode
+class alignas(8) TypeSourceInfo {
+  // Contains a memory block after the class, used for type source information,
+  // allocated by ASTContext.
+  friend class ASTContext;
+
+  QualType Ty;
+
+  TypeSourceInfo(QualType ty) : Ty(ty) {}
+
+public:
+  /// Return the type wrapped by this type source info.
+  QualType getType() const { return Ty; }
+
+  /// Return the TypeLoc wrapper for the type source info.
+  TypeLoc getTypeLoc() const; // implemented in TypeLoc.h
+
+  /// Override the type stored in this TypeSourceInfo. Use with caution!
+  void overrideType(QualType T) { Ty = T; }
+};
+
 // Inline function definitions.
 
 inline SplitQualType SplitQualType::getSingleStepDesugaredType() const {
diff --git a/clang/include/clang/AST/TypeLoc.h b/clang/include/clang/AST/TypeLoc.h
--- a/clang/include/clang/AST/TypeLoc.h
+++ b/clang/include/clang/AST/TypeLoc.h
@@ -14,7 +14,6 @@
 #ifndef LLVM_CLANG_AST_TYPELOC_H
 #define LLVM_CLANG_AST_TYPELOC_H
 
-#include "clang/AST/Decl.h"
 #include "clang/AST/NestedNameSpecifier.h"
 #include "clang/AST/TemplateBase.h"
 #include "clang/AST/Type.h"
@@ -39,6 +38,7 @@
 class ObjCInterfaceDecl;
 class ObjCProtocolDecl;
 class ObjCTypeParamDecl;
+class ParmVarDecl;
 class TemplateTypeParmDecl;
 class UnqualTypeLoc;
 class UnresolvedUsingTypenameDecl;
@@ -704,11 +704,7 @@
   TagDecl *getDecl() const { return getTypePtr()->getDecl(); }
 
   /// True if the tag was defined in this type specifier.
-  bool isDefinition() const {
-    TagDecl *D = getDecl();
-    return D->isCompleteDefinition() &&
-           (D->getIdentifier() == nullptr || D->getLocation() == getNameLoc());
-  }
+  bool isDefinition() const;
 };
 
 /// Wrapper for source info for record types.
diff --git a/clang/lib/AST/TypeLoc.cpp b/clang/lib/AST/TypeLoc.cpp
--- a/clang/lib/AST/TypeLoc.cpp
+++ b/clang/lib/AST/TypeLoc.cpp
@@ -294,6 +294,12 @@
   return TSTChecker().Visit(TL);
 }
 
+bool TagTypeLoc::isDefinition() const {
+  TagDecl *D = getDecl();
+  return D->isCompleteDefinition() &&
+         (D->getIdentifier() == nullptr || D->getLocation() == getNameLoc());
+}
+
 // Reimplemented to account for GNU/C++ extension
 //     typeof unary-expression
 // where there are no parentheses.