diff --git a/generator/annotator.cpp b/generator/annotator.cpp
index a07bb69..a9f532f 100644
--- a/generator/annotator.cpp
+++ b/generator/annotator.cpp
@@ -50,6 +50,7 @@
 
 #include "stringbuilder.h"
 #include "projectmanager.h"
+#include "compat.h"
 
 namespace
 {
@@ -1091,14 +1092,14 @@ void Annotator::syntaxHighlight(Generator &generator, clang::FileID FID, clang::
                 // Chop off the u part of u8 prefix
                 ++TokOffs;
                 --TokLen;
-                // FALL THROUGH to chop the 8
+                LLVM_FALLTHROUGH;
             case tok::wide_string_literal:
             case tok::utf16_string_literal:
             case tok::utf32_string_literal:
                 // Chop off the L, u, U or 8 prefix
                 ++TokOffs;
                 --TokLen;
-                // FALL THROUGH.
+                LLVM_FALLTHROUGH;
             case tok::string_literal:
                 // FIXME: Exclude the optional ud-suffix from the highlighted range.
                 generator.addTag("q", {}, TokOffs, TokLen);
@@ -1109,6 +1110,7 @@ void Annotator::syntaxHighlight(Generator &generator, clang::FileID FID, clang::
             case tok::utf32_char_constant:
                 ++TokOffs;
                 --TokLen;
+                LLVM_FALLTHROUGH;
             case tok::char_constant:
                 generator.addTag("kbd", {}, TokOffs, TokLen);
                 break;
diff --git a/generator/compat.h b/generator/compat.h
index 4446565..2814cef 100644
--- a/generator/compat.h
+++ b/generator/compat.h
@@ -31,3 +31,7 @@ template<typename T> struct MaybeUnique {
 };
 template<typename T> MaybeUnique<T> maybe_unique(T* val) { return {val}; }
 
+#ifndef LLVM_FALLTHROUGH
+#define LLVM_FALLTHROUGH
+#endif
+
diff --git a/generator/main.cpp b/generator/main.cpp
index d7afc6e..c3dacf1 100644
--- a/generator/main.cpp
+++ b/generator/main.cpp
@@ -127,6 +127,7 @@ struct BrowserDiagnosticClient : clang::DiagnosticConsumer {
         switch(DiagLevel) {
             case clang::DiagnosticsEngine::Fatal:
                 std::cerr << "FATAL ";
+                LLVM_FALLTHROUGH;
             case clang::DiagnosticsEngine::Error:
                 std::cerr << "Error: " << locationToString(Info.getLocation(), annotator.getSourceMgr())
                             << ": " << diag.c_str() << std::endl;
@@ -304,8 +305,17 @@ static bool proceedCommand(std::vector<std::string> command, llvm::StringRef Dir
 }
 
 int main(int argc, const char **argv) {
+    std::string ErrorMessage;
     std::unique_ptr<clang::tooling::CompilationDatabase> Compilations(
-        clang::tooling::FixedCompilationDatabase::loadFromCommandLine(argc, argv));
+        clang::tooling::FixedCompilationDatabase::loadFromCommandLine(argc, argv
+#if CLANG_VERSION_MAJOR >= 5
+       , ErrorMessage
+#endif
+        ));
+    if (!ErrorMessage.empty()) {
+        std::cerr << ErrorMessage << std::endl;
+        ErrorMessage = {};
+    }
 
     llvm::cl::ParseCommandLineOptions(argc, argv);
 
@@ -341,7 +351,6 @@ int main(int argc, const char **argv) {
 
 
     if (!Compilations && llvm::sys::fs::exists(BuildPath)) {
-        std::string ErrorMessage;
         if (llvm::sys::fs::is_directory(BuildPath)) {
             Compilations = std::unique_ptr<clang::tooling::CompilationDatabase>(
                 clang::tooling::CompilationDatabase::loadFromDirectory(BuildPath, ErrorMessage));
diff --git a/generator/preprocessorcallback.cpp b/generator/preprocessorcallback.cpp
index 45bc9d1..1e4d9b8 100644
--- a/generator/preprocessorcallback.cpp
+++ b/generator/preprocessorcallback.cpp
@@ -188,7 +188,11 @@ void PreprocessorCallback::MacroDefined(const clang::Token& MacroNameTok, const
     annotator.generator(FID).addTag("dfn", "class=\"macro\" id=\""% ref %"\" data-ref=\"" % ref % "\"", sm.getFileOffset(loc), MacroNameTok.getLength());
 }
 
-void PreprocessorCallback::MacroUndefined(const clang::Token& MacroNameTok, PreprocessorCallback::MyMacroDefinition MD)
+void PreprocessorCallback::MacroUndefined(const clang::Token& MacroNameTok, PreprocessorCallback::MyMacroDefinition MD
+#if CLANG_VERSION_MAJOR >= 5
+       , const clang::MacroDirective *
+#endif
+            )
 {
     clang::SourceLocation loc = MacroNameTok.getLocation();
     if (!loc.isValid() || !loc.isFileID())
diff --git a/generator/preprocessorcallback.h b/generator/preprocessorcallback.h
index b7925ee..d1c6549 100644
--- a/generator/preprocessorcallback.h
+++ b/generator/preprocessorcallback.h
@@ -54,7 +54,11 @@ class PreprocessorCallback  : public clang::PPCallbacks {
 
     void MacroDefined(const clang::Token &MacroNameTok, const clang::MacroDirective *MD) override;
 
-    void MacroUndefined(const clang::Token &MacroNameTok, MyMacroDefinition MD) override;
+    void MacroUndefined(const clang::Token &MacroNameTok, MyMacroDefinition MD
+#if CLANG_VERSION_MAJOR >= 5
+       , const clang::MacroDirective *
+#endif
+        ) override;
 
     bool FileNotFound(llvm::StringRef FileName, llvm::SmallVectorImpl<char> &RecoveryPath) override;
     void InclusionDirective(clang::SourceLocation HashLoc, const clang::Token& IncludeTok, llvm::StringRef FileName,