diff --git a/clang-tools-extra/clang-doc/BitcodeReader.cpp b/clang-tools-extra/clang-doc/BitcodeReader.cpp
--- a/clang-tools-extra/clang-doc/BitcodeReader.cpp
+++ b/clang-tools-extra/clang-doc/BitcodeReader.cpp
@@ -259,6 +259,8 @@
   switch (ID) {
   case FIELD_TYPE_NAME:
     return decodeRecord(R, I->Name, Blob);
+  case FIELD_DEFAULT_VALUE:
+    return decodeRecord(R, I->DefaultValue, Blob);
   default:
     return llvm::createStringError(llvm::inconvertibleErrorCode(),
                                    "invalid field for TypeInfo");
diff --git a/clang-tools-extra/clang-doc/BitcodeWriter.h b/clang-tools-extra/clang-doc/BitcodeWriter.h
--- a/clang-tools-extra/clang-doc/BitcodeWriter.h
+++ b/clang-tools-extra/clang-doc/BitcodeWriter.h
@@ -88,6 +88,7 @@
   COMMENT_ATTRVAL,
   COMMENT_ARG,
   FIELD_TYPE_NAME,
+  FIELD_DEFAULT_VALUE,
   MEMBER_TYPE_NAME,
   MEMBER_TYPE_ACCESS,
   NAMESPACE_USR,
diff --git a/clang-tools-extra/clang-doc/BitcodeWriter.cpp b/clang-tools-extra/clang-doc/BitcodeWriter.cpp
--- a/clang-tools-extra/clang-doc/BitcodeWriter.cpp
+++ b/clang-tools-extra/clang-doc/BitcodeWriter.cpp
@@ -148,6 +148,7 @@
           {COMMENT_ATTRVAL, {"AttrVal", &StringAbbrev}},
           {COMMENT_ARG, {"Arg", &StringAbbrev}},
           {FIELD_TYPE_NAME, {"Name", &StringAbbrev}},
+          {FIELD_DEFAULT_VALUE, {"DefaultValue", &StringAbbrev}},
           {MEMBER_TYPE_NAME, {"Name", &StringAbbrev}},
           {MEMBER_TYPE_ACCESS, {"Access", &IntAbbrev}},
           {NAMESPACE_USR, {"USR", &SymbolIDAbbrev}},
@@ -207,7 +208,7 @@
         // Type Block
         {BI_TYPE_BLOCK_ID, {}},
         // FieldType Block
-        {BI_FIELD_TYPE_BLOCK_ID, {FIELD_TYPE_NAME}},
+        {BI_FIELD_TYPE_BLOCK_ID, {FIELD_TYPE_NAME, FIELD_DEFAULT_VALUE}},
         // MemberType Block
         {BI_MEMBER_TYPE_BLOCK_ID, {MEMBER_TYPE_NAME, MEMBER_TYPE_ACCESS}},
         // Enum Block
@@ -419,6 +420,7 @@
   StreamSubBlockGuard Block(Stream, BI_FIELD_TYPE_BLOCK_ID);
   emitBlock(T.Type, FieldId::F_type);
   emitRecord(T.Name, FIELD_TYPE_NAME);
+  emitRecord(T.DefaultValue, FIELD_DEFAULT_VALUE);
 }
 
 void ClangDocBitcodeWriter::emitBlock(const MemberTypeInfo &T) {
diff --git a/clang-tools-extra/clang-doc/Representation.h b/clang-tools-extra/clang-doc/Representation.h
--- a/clang-tools-extra/clang-doc/Representation.h
+++ b/clang-tools-extra/clang-doc/Representation.h
@@ -181,10 +181,15 @@
       : TypeInfo(RefName, Path), Name(Name) {}
 
   bool operator==(const FieldTypeInfo &Other) const {
-    return std::tie(Type, Name) == std::tie(Other.Type, Other.Name);
+    return std::tie(Type, Name, DefaultValue) ==
+           std::tie(Other.Type, Other.Name, Other.DefaultValue);
   }
 
   SmallString<16> Name; // Name associated with this info.
+
+  // When used for function parameters, contains the string representing the
+  // expression of the default value, if any.
+  SmallString<16> DefaultValue;
 };
 
 // Info for member types.
diff --git a/clang-tools-extra/clang-doc/Serialize.cpp b/clang-tools-extra/clang-doc/Serialize.cpp
--- a/clang-tools-extra/clang-doc/Serialize.cpp
+++ b/clang-tools-extra/clang-doc/Serialize.cpp
@@ -10,6 +10,7 @@
 #include "BitcodeWriter.h"
 #include "clang/AST/Comment.h"
 #include "clang/Index/USRGeneration.h"
+#include "clang/Lex/Lexer.h"
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/SHA1.h"
@@ -310,21 +311,31 @@
 
 static void parseParameters(FunctionInfo &I, const FunctionDecl *D) {
   for (const ParmVarDecl *P : D->parameters()) {
+    FieldTypeInfo *FieldInfo = nullptr;
     if (const auto *T = getDeclForType(P->getOriginalType())) {
       if (const auto *N = dyn_cast<EnumDecl>(T)) {
-        I.Params.emplace_back(getUSRForDecl(N), N->getNameAsString(),
-                              InfoType::IT_enum, getInfoRelativePath(N),
-                              P->getNameAsString());
-        continue;
+        FieldInfo = &I.Params.emplace_back(
+            getUSRForDecl(N), N->getNameAsString(), InfoType::IT_enum,
+            getInfoRelativePath(N), P->getNameAsString());
       } else if (const auto *N = dyn_cast<RecordDecl>(T)) {
-        I.Params.emplace_back(getUSRForDecl(N), N->getNameAsString(),
-                              InfoType::IT_record, getInfoRelativePath(N),
-                              P->getNameAsString());
-        continue;
+        FieldInfo = &I.Params.emplace_back(
+            getUSRForDecl(N), N->getNameAsString(), InfoType::IT_record,
+            getInfoRelativePath(N), P->getNameAsString());
       }
+      // Otherwise fall through to the default case below.
+    }
+
+    if (!FieldInfo) {
+      FieldInfo = &I.Params.emplace_back(P->getOriginalType().getAsString(),
+                                         P->getNameAsString());
+    }
+
+    if (const Expr *DefaultArg = P->getDefaultArg()) {
+      FieldInfo->DefaultValue = Lexer::getSourceText(
+          CharSourceRange::getTokenRange(DefaultArg->getSourceRange()),
+          D->getASTContext().getSourceManager(),
+          D->getASTContext().getLangOpts());
     }
-    I.Params.emplace_back(P->getOriginalType().getAsString(),
-                          P->getNameAsString());
   }
 }
 
diff --git a/clang-tools-extra/clang-doc/YAMLGenerator.cpp b/clang-tools-extra/clang-doc/YAMLGenerator.cpp
--- a/clang-tools-extra/clang-doc/YAMLGenerator.cpp
+++ b/clang-tools-extra/clang-doc/YAMLGenerator.cpp
@@ -109,6 +109,7 @@
 static void FieldTypeInfoMapping(IO &IO, FieldTypeInfo &I) {
   TypeInfoMapping(IO, I);
   IO.mapOptional("Name", I.Name, SmallString<16>());
+  IO.mapOptional("DefaultValue", I.DefaultValue, SmallString<16>());
 }
 
 static void InfoMapping(IO &IO, Info &I) {
@@ -183,6 +184,7 @@
   static void mapping(IO &IO, FieldTypeInfo &I) {
     TypeInfoMapping(IO, I);
     IO.mapOptional("Name", I.Name, SmallString<16>());
+    IO.mapOptional("DefaultValue", I.DefaultValue, SmallString<16>());
   }
 };
 
diff --git a/clang-tools-extra/unittests/clang-doc/SerializeTest.cpp b/clang-tools-extra/unittests/clang-doc/SerializeTest.cpp
--- a/clang-tools-extra/unittests/clang-doc/SerializeTest.cpp
+++ b/clang-tools-extra/unittests/clang-doc/SerializeTest.cpp
@@ -511,7 +511,7 @@
   std::vector<std::string> Args;
   Args.push_back("-fmodules-ts");
   ExtractInfosFromCodeWithArgs(R"raw(export module M;
-int moduleFunction(int x);
+int moduleFunction(int x, double d = 3.2 - 1.0);
 static int staticModuleFunction(int x);
 export double exportedModuleFunction(double y);)raw",
                                2, /*Public=*/true, Infos, Args);
@@ -523,6 +523,8 @@
   F.ReturnType = TypeInfo(EmptySID, "int", InfoType::IT_default);
   F.Loc.emplace_back(0, llvm::SmallString<16>{"test.cpp"});
   F.Params.emplace_back("int", "x");
+  F.Params.emplace_back("double", "d");
+  F.Params.back().DefaultValue = "3.2 - 1.0";
   F.Access = AccessSpecifier::AS_none;
   ExpectedBWithFunction.ChildFunctions.emplace_back(std::move(F));
   CheckNamespaceInfo(&ExpectedBWithFunction, BWithFunction);
diff --git a/clang-tools-extra/unittests/clang-doc/YAMLGeneratorTest.cpp b/clang-tools-extra/unittests/clang-doc/YAMLGeneratorTest.cpp
--- a/clang-tools-extra/unittests/clang-doc/YAMLGeneratorTest.cpp
+++ b/clang-tools-extra/unittests/clang-doc/YAMLGeneratorTest.cpp
@@ -209,6 +209,8 @@
   I.ReturnType =
       TypeInfo(EmptySID, "void", InfoType::IT_default, "path/to/void");
   I.Params.emplace_back("int", "path/to/int", "P");
+  I.Params.emplace_back("double", "path/to/double", "D");
+  I.Params.back().DefaultValue = "2.0 * M_PI";
   I.IsMethod = true;
   I.Parent = Reference(EmptySID, "Parent", InfoType::IT_record);
 
@@ -240,6 +242,11 @@
       Name:            'int'
       Path:            'path/to/int'
     Name:            'P'
+  - Type:
+      Name:            'double'
+      Path:            'path/to/double'
+    Name:            'D'
+    DefaultValue:    '2.0 * M_PI'
 ReturnType:
   Type:
     Name:            'void'