diff --git a/CMakeLists.txt b/CMakeLists.txt
index ae6cfdb..b135805 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -41,8 +41,9 @@ find_package(LLVM REQUIRED CONFIG)
 message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
 message(STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR}")
 
-if((${LLVM_PACKAGE_VERSION} VERSION_LESS "9.0.0")
+if(((${LLVM_PACKAGE_VERSION} VERSION_LESS "9.0.0")
    OR (${LLVM_PACKAGE_VERSION} VERSION_GREATER_EQUAL "12"))
+   AND (NOT (${LLVM_PACKAGE_VERSION} VERSION_EQUAL "13")))
   message(FATAL_ERROR "Only LLVM 9 through 11 are supported.")
 endif()
 
diff --git a/main.cpp b/main.cpp
index 0753191..6735b5c 100644
--- a/main.cpp
+++ b/main.cpp
@@ -235,6 +235,9 @@ class ConstexprFunctionASTVisitor
 #if LLVM_VERSION_MAJOR <= 9
       if (!sema.CheckConstexprFunctionBody(func, func->getBody()))
         return true;
+#elif LLVM_VERSION_MAJOR == 13
+      if(!sema.CheckConstexprFunctionDefinition(func, Sema::CheckConstexprKind::CheckValid))
+        return true;
 #endif
 
       if (!CheckConstexprParameterTypes(sema, func))
@@ -247,7 +250,11 @@ class ConstexprFunctionASTVisitor
 
     // Mark function as constexpr, the next ast visitor will use this
     // information to find constexpr vardecls
+#if LLVM_VERSION_MAJOR == 13
+    func->setConstexprKind(ConstexprSpecKind::Constexpr);
+#else
     func->setConstexprKind(CSK_constexpr);
+#endif
 
     // Create diagnostic
     const auto FixIt = clang::FixItHint::CreateInsertion(loc, "constexpr ");
@@ -305,9 +312,11 @@ class ConstexprVarDeclFunctionASTVisitor
       if (!ty.isConstQualified())
         return true;
 
+#if LLVM_VERSION_MAJOR != 13
       // Is init an integral constant expression
       if (!var->checkInitIsICE())
         return true;
+#endif
 
       // Does the init function use dependent values
       if (Init->isValueDependent())
@@ -317,9 +326,17 @@ class ConstexprVarDeclFunctionASTVisitor
       if (!var->evaluateValue())
         return true;
 
+#if LLVM_VERSION_MAJOR == 13
+      if(!var->hasConstantInitialization())
+        return true;
+
+      if (!var->hasICEInitializer(CI_.getASTContext()))
+        return true;
+#else
       // Is init an ice
       if (!var->isInitICE())
         return true;
+#endif
 
       // Create Diagnostic/FixIt
       const auto FixIt = clang::FixItHint::CreateInsertion(loc, "constexpr ");
@@ -410,8 +427,19 @@ class FunctionDeclFrontendAction : public clang::ASTFrontendAction {
 };
 
 int main(int argc, const char **argv) {
+
+#if LLVM_VERSION_MAJOR == 13
+  auto ExpectedParser = CommonOptionsParser::create(argc, argv, ConstexprCategory);
+  if (!ExpectedParser) {
+    llvm::errs() << ExpectedParser.takeError();
+    return 1;
+  }
+  CommonOptionsParser& OptionsParser = ExpectedParser.get();
+#else
   CommonOptionsParser OptionsParser(argc, argv, ConstexprCategory);
 
+#endif
+
   ClangTool Tool(OptionsParser.getCompilations(),
                  OptionsParser.getSourcePathList());
   Tool.run(newFrontendActionFactory<FunctionDeclFrontendAction>().get());