diff --git a/clang-tools-extra/clang-tidy/ClangTidy.cpp b/clang-tools-extra/clang-tidy/ClangTidy.cpp
index f4ab93b51f4a7..68192f7ad6240 100644
--- a/clang-tools-extra/clang-tidy/ClangTidy.cpp
+++ b/clang-tools-extra/clang-tidy/ClangTidy.cpp
@@ -417,6 +417,9 @@ ClangTidyASTConsumerFactory::createASTConsumer(
 
   ast_matchers::MatchFinder::MatchFinderOptions FinderOptions;
 
+  // We should always skip the declarations in modules.
+  FinderOptions.SkipDeclsInModules = true;
+
   std::unique_ptr<ClangTidyProfiling> Profiling;
   if (Context.getEnableProfiling()) {
     Profiling =
diff --git a/clang-tools-extra/test/clang-tidy/infrastructure/cxx20-modules.cppm b/clang-tools-extra/test/clang-tidy/infrastructure/cxx20-modules.cppm
new file mode 100644
index 0000000000000..b7e39e2295a1f
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/infrastructure/cxx20-modules.cppm
@@ -0,0 +1,29 @@
+// RUN: rm -fr %t
+// RUN: mkdir %t
+// RUN: split-file %s %t
+// RUN: mkdir %t/tmp
+//
+// RUN: %check_clang_tidy -std=c++20 -check-suffix=DEFAULT %t/a.cpp \
+// RUN:   cppcoreguidelines-narrowing-conversions %t/a.cpp -- \
+// RUN:   -config='{}'
+
+// RUN: %clang -std=c++20 -x c++-module %t/a.cpp --precompile -o %t/a.pcm
+
+// RUN: %check_clang_tidy -std=c++20 -check-suffix=DEFAULT %t/use.cpp \
+// RUN:   cppcoreguidelines-narrowing-conversions %t/a.cpp -- \
+// RUN:   -config='{}' -- -fmodule-file=a=%t/a.pcm 
+
+//--- a.cpp
+export module a;
+export void most_narrowing_is_not_ok() {
+  int i;
+  long long ui;
+  i = ui;
+  // CHECK-MESSAGES-DEFAULT: :[[@LINE-1]]:7: warning: narrowing conversion from 'long long' to signed type 'int' is implementation-defined [cppcoreguidelines-narrowing-conversions]
+}
+
+//--- use.cpp
+import a;
+void use() {
+  most_narrowing_is_not_ok();
+}
diff --git a/clang-tools-extra/test/lit.cfg.py b/clang-tools-extra/test/lit.cfg.py
index 9f64fd3d2ffa2..73882851345bf 100644
--- a/clang-tools-extra/test/lit.cfg.py
+++ b/clang-tools-extra/test/lit.cfg.py
@@ -19,6 +19,7 @@
 config.suffixes = [
     ".c",
     ".cpp",
+    ".cppm",
     ".hpp",
     ".m",
     ".mm",
diff --git a/clang/include/clang/ASTMatchers/ASTMatchFinder.h b/clang/include/clang/ASTMatchers/ASTMatchFinder.h
index 73cbcf1f25025..69d569a7b09cc 100644
--- a/clang/include/clang/ASTMatchers/ASTMatchFinder.h
+++ b/clang/include/clang/ASTMatchers/ASTMatchFinder.h
@@ -139,6 +139,11 @@ class MatchFinder {
     ///
     /// It prints a report after match.
     std::optional<Profiling> CheckProfiling;
+
+    bool SkipDeclsInModules = false;
+
+    MatchFinderOptions()
+        : CheckProfiling(std::nullopt), SkipDeclsInModules(false) {}
   };
 
   MatchFinder(MatchFinderOptions Options = MatchFinderOptions());
diff --git a/clang/lib/ASTMatchers/ASTMatchFinder.cpp b/clang/lib/ASTMatchers/ASTMatchFinder.cpp
index 6d0ba0b7907a1..d35565bdb257f 100644
--- a/clang/lib/ASTMatchers/ASTMatchFinder.cpp
+++ b/clang/lib/ASTMatchers/ASTMatchFinder.cpp
@@ -20,6 +20,7 @@
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/RecursiveASTVisitor.h"
+#include "clang/Basic/Module.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/StringMap.h"
@@ -1469,6 +1470,9 @@ bool MatchASTVisitor::TraverseDecl(Decl *DeclNode) {
     return true;
   }
 
+  if (Options.SkipDeclsInModules && DeclNode->isInAnotherModuleUnit())
+    return true;
+
   bool ScopedTraversal =
       TraversingASTNodeNotSpelledInSource || DeclNode->isImplicit();
   bool ScopedChildren = TraversingASTChildrenNotSpelledInSource;