diff --git a/lldb/source/Target/PathMappingList.cpp b/lldb/source/Target/PathMappingList.cpp
--- a/lldb/source/Target/PathMappingList.cpp
+++ b/lldb/source/Target/PathMappingList.cpp
@@ -152,6 +152,18 @@
   return false;
 }
 
+/// Append components to path, applying style.
+static void AppendPathComponents(FileSpec &path, llvm::StringRef components,
+                                 llvm::sys::path::Style style) {
+    auto component = llvm::sys::path::begin(components, style);
+    auto e = llvm::sys::path::end(components);
+    while (component != e &&
+        llvm::sys::path::is_separator(*component->data(), style))
+      ++component;
+    for (; component != e; ++component)
+      path.AppendPathComponent(*component);
+}
+
 llvm::Optional<FileSpec>
 PathMappingList::RemapPath(llvm::StringRef path) const {
   if (m_pairs.empty() || path.empty())
@@ -175,7 +187,9 @@
         continue;
     }
     FileSpec remapped(it.second.GetStringRef());
-    remapped.AppendPathComponent(path);
+    auto orig_style = FileSpec::GuessPathStyle(prefix).getValueOr(
+        llvm::sys::path::Style::native);
+    AppendPathComponents(remapped, path, orig_style);
     return remapped;
   }
   return {};
@@ -187,8 +201,11 @@
   for (const auto &it : m_pairs) {
     if (!path_ref.consume_front(it.second.GetStringRef()))
       continue;
-    fixed.SetFile(it.first.GetStringRef(), FileSpec::Style::native);
-    fixed.AppendPathComponent(path_ref);
+    auto orig_file = it.first.GetStringRef();
+    auto orig_style = FileSpec::GuessPathStyle(orig_file).getValueOr(
+        llvm::sys::path::Style::native);
+    fixed.SetFile(orig_file, orig_style);
+    AppendPathComponents(fixed, path_ref, orig_style);
     return true;
   }
   return false;
diff --git a/lldb/unittests/Target/PathMappingListTest.cpp b/lldb/unittests/Target/PathMappingListTest.cpp
--- a/lldb/unittests/Target/PathMappingListTest.cpp
+++ b/lldb/unittests/Target/PathMappingListTest.cpp
@@ -6,9 +6,9 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/ADT/ArrayRef.h"
 #include "lldb/Target/PathMappingList.h"
 #include "lldb/Utility/FileSpec.h"
+#include "llvm/ADT/ArrayRef.h"
 #include "gtest/gtest.h"
 #include <utility>
 
@@ -19,6 +19,8 @@
   FileSpec original;
   FileSpec remapped;
   Matches(const char *o, const char *r) : original(o), remapped(r) {}
+  Matches(const char *o, llvm::sys::path::Style style, const char *r)
+      : original(o, style), remapped(r) {}
 };
 } // namespace
 
@@ -112,3 +114,27 @@
   };
   TestPathMappings(map, matches, fails);
 }
+
+#ifndef _WIN32
+TEST(PathMappingListTest, CrossPlatformTests) {
+  PathMappingList map;
+  map.Append(ConstString(R"(C:\old)"), ConstString("/new"), false);
+  Matches matches[] = {
+    {R"(C:\old)", llvm::sys::path::Style::windows, "/new"},
+    {R"(C:\old\)", llvm::sys::path::Style::windows, "/new"},
+    {R"(C:\old\foo\.)", llvm::sys::path::Style::windows, "/new/foo"},
+    {R"(C:\old\foo.c)", llvm::sys::path::Style::windows, "/new/foo.c"},
+    {R"(C:\old\foo.c\.)", llvm::sys::path::Style::windows, "/new/foo.c"},
+    {R"(C:\old\.\foo.c)", llvm::sys::path::Style::windows, "/new/foo.c"},
+  };
+  ConstString fails[] = {
+    ConstString("/foo"),
+    ConstString("/"),
+    ConstString("foo.c"),
+    ConstString("./foo.c"),
+    ConstString("../foo.c"),
+    ConstString("../bar/foo.c"),
+  };
+  TestPathMappings(map, matches, fails);
+}
+#endif