diff --git a/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp b/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp
--- a/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp
+++ b/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp
@@ -15,6 +15,7 @@
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallString.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include <string>
@@ -73,16 +74,20 @@
 
 tooling::CompileCommand
 GlobalCompilationDatabase::getFallbackCommand(PathRef File) const {
+  llvm::SmallString<128> CanonPath(File);
+  llvm::sys::path::remove_dots(CanonPath, true);
+
   std::vector<std::string> Argv = {getFallbackClangPath()};
   // Clang treats .h files as C by default and files without extension as linker
   // input, resulting in unhelpful diagnostics.
   // Parsing as Objective C++ is friendly to more cases.
-  auto FileExtension = llvm::sys::path::extension(File);
+  auto FileExtension = llvm::sys::path::extension(CanonPath);
   if (FileExtension.empty() || FileExtension == ".h")
     Argv.push_back("-xobjective-c++-header");
-  Argv.push_back(File);
-  tooling::CompileCommand Cmd(llvm::sys::path::parent_path(File),
-                              llvm::sys::path::filename(File), std::move(Argv),
+  Argv.push_back(CanonPath.str().str());
+  tooling::CompileCommand Cmd(llvm::sys::path::parent_path(CanonPath),
+                              llvm::sys::path::filename(CanonPath),
+                              std::move(Argv),
                               /*Output=*/"");
   Cmd.Heuristic = "clangd fallback";
   return Cmd;
@@ -136,6 +141,8 @@
     CDBLookupRequest Request) const {
   assert(llvm::sys::path::is_absolute(Request.FileName) &&
          "path must be absolute");
+  llvm::SmallString<128> CanonPath(Request.FileName);
+  llvm::sys::path::remove_dots(CanonPath, true);
 
   CDBLookupResult Result;
   bool SentBroadcast = false;
@@ -148,7 +155,7 @@
       Result.PI.SourceRoot = *CompileCommandsDir;
     } else {
       actOnAllParentDirectories(
-          Request.FileName, [this, &SentBroadcast, &Result](PathRef Path) {
+          CanonPath, [this, &SentBroadcast, &Result](PathRef Path) {
             std::tie(Result.CDB, SentBroadcast) = getCDBInDirLocked(Path);
             Result.PI.SourceRoot = Path;
             return Result.CDB != nullptr;
@@ -203,13 +210,17 @@
   }
 
   std::vector<std::string> GovernedFiles;
+  llvm::SmallString<128> CanonPath;
   for (llvm::StringRef File : AllFiles) {
     // A file is governed by this CDB if lookup for the file would find it.
     // Independent of whether it has an entry for that file or not.
     actOnAllParentDirectories(File, [&](PathRef Path) {
       if (DirectoryHasCDB.lookup(Path)) {
-        if (Path == Result.PI.SourceRoot)
-          GovernedFiles.push_back(File);
+        if (Path == Result.PI.SourceRoot) {
+          CanonPath = File;
+          llvm::sys::path::remove_dots(CanonPath, true);
+          GovernedFiles.push_back(CanonPath.str().str());
+        }
         // Stop as soon as we hit a CDB.
         return true;
       }
@@ -245,10 +256,12 @@
 
 llvm::Optional<tooling::CompileCommand>
 OverlayCDB::getCompileCommand(PathRef File) const {
+  llvm::SmallString<128> CanonPath(File);
+  llvm::sys::path::remove_dots(CanonPath, true);
   llvm::Optional<tooling::CompileCommand> Cmd;
   {
     std::lock_guard<std::mutex> Lock(Mutex);
-    auto It = Commands.find(File);
+    auto It = Commands.find(CanonPath);
     if (It != Commands.end())
       Cmd = It->second;
   }
@@ -272,20 +285,24 @@
 
 void OverlayCDB::setCompileCommand(
     PathRef File, llvm::Optional<tooling::CompileCommand> Cmd) {
+  llvm::SmallString<128> CanonPath(File);
+  llvm::sys::path::remove_dots(CanonPath, true);
   {
     std::unique_lock<std::mutex> Lock(Mutex);
     if (Cmd)
-      Commands[File] = std::move(*Cmd);
+      Commands[CanonPath] = std::move(*Cmd);
     else
-      Commands.erase(File);
+      Commands.erase(CanonPath);
   }
-  OnCommandChanged.broadcast({File});
+  OnCommandChanged.broadcast({CanonPath.str().str()});
 }
 
 llvm::Optional<ProjectInfo> OverlayCDB::getProjectInfo(PathRef File) const {
+  llvm::SmallString<128> CanonPath(File);
+  llvm::sys::path::remove_dots(CanonPath, true);
   {
     std::lock_guard<std::mutex> Lock(Mutex);
-    auto It = Commands.find(File);
+    auto It = Commands.find(CanonPath);
     if (It != Commands.end())
       return ProjectInfo{};
   }
diff --git a/clang-tools-extra/clangd/unittests/GlobalCompilationDatabaseTests.cpp b/clang-tools-extra/clangd/unittests/GlobalCompilationDatabaseTests.cpp
--- a/clang-tools-extra/clangd/unittests/GlobalCompilationDatabaseTests.cpp
+++ b/clang-tools-extra/clangd/unittests/GlobalCompilationDatabaseTests.cpp
@@ -10,6 +10,7 @@
 
 #include "Path.h"
 #include "TestFS.h"
+#include "clang/Tooling/CompilationDatabase.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringExtras.h"
@@ -31,6 +32,7 @@
 using ::testing::Contains;
 using ::testing::ElementsAre;
 using ::testing::EndsWith;
+using ::testing::HasSubstr;
 using ::testing::IsEmpty;
 using ::testing::Not;
 using ::testing::StartsWith;
@@ -247,9 +249,10 @@
         });
 
     File = FS.Root;
-    llvm::sys::path::append(File, "a.cc");
+    llvm::sys::path::append(File, "build", "..", "a.cc");
     DB.getCompileCommand(File.str());
-    EXPECT_THAT(DiscoveredFiles, UnorderedElementsAre(EndsWith("a.cc")));
+    EXPECT_THAT(DiscoveredFiles, UnorderedElementsAre(AllOf(
+                                     EndsWith("a.cc"), Not(HasSubstr("..")))));
     DiscoveredFiles.clear();
 
     File = FS.Root;
@@ -282,6 +285,28 @@
   }
 }
 
+TEST(GlobalCompilationDatabaseTest, NonCanonicalFilenames) {
+  OverlayCDB DB(nullptr);
+  std::vector<std::string> DiscoveredFiles;
+  auto Sub =
+      DB.watch([&DiscoveredFiles](const std::vector<std::string> Changes) {
+        DiscoveredFiles = Changes;
+      });
+
+  llvm::SmallString<128> Root(testRoot());
+  llvm::sys::path::append(Root, "build", "..", "a.cc");
+  DB.setCompileCommand(Root.str(), tooling::CompileCommand());
+  EXPECT_THAT(DiscoveredFiles, UnorderedElementsAre(testPath("a.cc")));
+  DiscoveredFiles.clear();
+
+  llvm::SmallString<128> File(testRoot());
+  llvm::sys::path::append(File, "blabla", "..", "a.cc");
+
+  EXPECT_TRUE(DB.getCompileCommand(File));
+  EXPECT_TRUE(DB.getProjectInfo(File));
+  EXPECT_EQ(DB.getFallbackCommand(File).Directory, testRoot());
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang