diff --git a/llvm/test/tools/llvm-cxxfilt/coff-import.test b/llvm/test/tools/llvm-cxxfilt/coff-import.test
--- a/llvm/test/tools/llvm-cxxfilt/coff-import.test
+++ b/llvm/test/tools/llvm-cxxfilt/coff-import.test
@@ -1,5 +1,12 @@
 RUN: llvm-cxxfilt -_ ___imp__ZSt6futureIvE | FileCheck %s
 RUN: llvm-cxxfilt -n __imp__ZSt6futureIvE | FileCheck %s
 
-CHECK: import thunk for std::future<void>
+## This should not demangle
+RUN: llvm-cxxfilt -n __imp__foo | FileCheck %s --check-prefix=CHECK-STRING --match-full-lines
+
+RUN: echo "__imp__ZSt6futureIvE __imp__ZSt6futureIvE" | llvm-cxxfilt -n | \
+RUN:    FileCheck %s --check-prefix=CHECK-SPLIT
 
+CHECK: import thunk for std::future<void>
+CHECK-STRING: __imp__foo
+CHECK-SPLIT: import thunk for std::future<void> import thunk for std::future<void>
diff --git a/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp b/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp
--- a/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp
+++ b/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp
@@ -74,8 +74,9 @@
   return Triple(sys::getProcessTriple()).isOSBinFormatMachO();
 }
 
-static std::string demangle(llvm::raw_ostream &OS, const std::string &Mangled) {
+static std::string demangle(const std::string &Mangled) {
   int Status;
+  std::string Prefix;
 
   const char *DecoratedStr = Mangled.c_str();
   if (shouldStripUnderscore())
@@ -92,11 +93,11 @@
 
   if (!Undecorated &&
       (DecoratedLength > 6 && strncmp(DecoratedStr, "__imp_", 6) == 0)) {
-    OS << "import thunk for ";
+    Prefix = "import thunk for ";
     Undecorated = itaniumDemangle(DecoratedStr + 6, nullptr, nullptr, &Status);
   }
 
-  std::string Result(Undecorated ? Undecorated : Mangled);
+  std::string Result(Undecorated ? Prefix + Undecorated : Mangled);
   free(Undecorated);
   return Result;
 }
@@ -144,9 +145,9 @@
     SmallVector<std::pair<StringRef, StringRef>, 16> Words;
     SplitStringDelims(Mangled, Words, IsLegalItaniumChar);
     for (const auto &Word : Words)
-      Result += demangle(OS, Word.first) + Word.second.str();
+      Result += ::demangle(Word.first) + Word.second.str();
   } else
-    Result = demangle(OS, Mangled);
+    Result = ::demangle(Mangled);
   OS << Result << '\n';
   OS.flush();
 }