diff --git a/clang-tools-extra/clangd/CodeCompletionStrings.cpp b/clang-tools-extra/clangd/CodeCompletionStrings.cpp
--- a/clang-tools-extra/clangd/CodeCompletionStrings.cpp
+++ b/clang-tools-extra/clangd/CodeCompletionStrings.cpp
@@ -32,6 +32,21 @@
   }
 }
 
+void appendCodeCompletionString(const CodeCompletionString &CCS, std::string *Out) {
+  for (const CodeCompletionString::Chunk &C : CCS) {
+    switch (C.Kind) {
+    case CodeCompletionString::CK_Optional:
+      assert(C.Optional &&
+             "Expected the optional code completion string to be non-null.");
+      appendCodeCompletionString(*C.Optional, Out);
+      break;
+    default:
+      *Out += C.Text;
+      break;
+    }
+  }
+}
+
 bool looksLikeDocComment(llvm::StringRef CommentText) {
   // We don't report comments that only contain "special" chars.
   // This avoids reporting various delimiters, like:
@@ -138,6 +153,10 @@
       *Snippet += Chunk.Text;
       break;
     case CodeCompletionString::CK_Optional:
+      assert(Chunk.Optional &&
+             "Expected the optional code completion string to be non-null.");      
+      // No need to create placeholders for default arguments in Snippet.
+      appendCodeCompletionString(*Chunk.Optional, Signature);
       break;
     case CodeCompletionString::CK_Placeholder:
       *Signature += Chunk.Text;
diff --git a/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp b/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
--- a/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
+++ b/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
@@ -10,6 +10,7 @@
 #include "ClangdServer.h"
 #include "CodeComplete.h"
 #include "Compiler.h"
+#include "Logger.h"
 #include "Matchers.h"
 #include "Protocol.h"
 #include "Quality.h"
@@ -939,6 +940,25 @@
 
   EXPECT_TRUE(Results.Completions.empty());
 }
+
+TEST(CompletionTest, DefaultArgs) {
+  clangd::CodeCompleteOptions Opts;
+  std::string Context = R"cpp(
+    int X(int A = 0);
+    int Y(int A, int B = 0);
+    int Z(int A, int B = 0, int C = 0, int D = 0);
+  )cpp";
+  EXPECT_THAT(completions(Context + "int y = X^", {}, Opts).Completions,
+              UnorderedElementsAre(Labeled("X(int A = 0)")));
+  EXPECT_THAT(completions(Context + "int y = Y^", {}, Opts).Completions,
+              UnorderedElementsAre(AllOf(Labeled("Y(int A, int B = 0)"),
+                                         SnippetSuffix("(${1:int A})"))));
+  EXPECT_THAT(completions(Context + "int y = Z^", {}, Opts).Completions,
+              UnorderedElementsAre(
+                  AllOf(Labeled("Z(int A, int B = 0, int C = 0, int D = 0)"),
+                        SnippetSuffix("(${1:int A})"))));
+}
+
 SignatureHelp signatures(llvm::StringRef Text, Position Point,
                          std::vector<Symbol> IndexSymbols = {}) {
   std::unique_ptr<SymbolIndex> Index;