diff --git a/include/swift/AST/Decl.h b/include/swift/AST/Decl.h
index 792568c22d518..c691a16bd3b17 100644
--- a/include/swift/AST/Decl.h
+++ b/include/swift/AST/Decl.h
@@ -659,7 +659,7 @@ class alignas(1 << DeclAlignInBits) Decl : public ASTAllocated<Decl> {
     HasAnyUnavailableValues : 1
   );
 
-  SWIFT_INLINE_BITFIELD(ModuleDecl, TypeDecl, 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1,
+  SWIFT_INLINE_BITFIELD(ModuleDecl, TypeDecl, 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1,
     /// If the module is compiled as static library.
     StaticLibrary : 1,
 
@@ -709,7 +709,10 @@ class alignas(1 << DeclAlignInBits) Decl : public ASTAllocated<Decl> {
 
     /// If the map from @objc provided name to top level swift::Decl in this
     /// module is populated
-    ObjCNameLookupCachePopulated : 1
+    ObjCNameLookupCachePopulated : 1,
+
+    /// Whether this module has been built with C++ interoperability enabled.
+    HasCxxInteroperability : 1
   );
 
   SWIFT_INLINE_BITFIELD(PrecedenceGroupDecl, Decl, 1+2,
diff --git a/include/swift/AST/DiagnosticsSema.def b/include/swift/AST/DiagnosticsSema.def
index 314bfab93b424..f5bd8f400f2a0 100644
--- a/include/swift/AST/DiagnosticsSema.def
+++ b/include/swift/AST/DiagnosticsSema.def
@@ -874,6 +874,12 @@ ERROR(need_hermetic_seal_to_import_module,none,
       "module %0 was built with -experimental-hermetic-seal-at-link, but "
       "current compilation does not have -experimental-hermetic-seal-at-link",
       (Identifier))
+ERROR(need_cxx_interop_to_import_module,none,
+      "module %0 was built with C++ interoperability enabled, but "
+      "current compilation does not enable C++ interoperability",
+      (Identifier))
+NOTE(enable_cxx_interop_docs,none,
+     "visit https://www.swift.org/documentation/cxx-interop/project-build-setup to learn how to enable C++ interoperability", ())
 
 ERROR(modularization_issue_decl_moved,Fatal,
       "reference to %select{top-level declaration|type}0 %1 broken by a context change; "
diff --git a/include/swift/AST/Module.h b/include/swift/AST/Module.h
index b15b881b5bf29..b1f0c7f6a24a9 100644
--- a/include/swift/AST/Module.h
+++ b/include/swift/AST/Module.h
@@ -654,6 +654,14 @@ class ModuleDecl
     Bits.ModuleDecl.HasHermeticSealAtLink = enabled;
   }
 
+  /// Returns true if this module was built with C++ interoperability enabled.
+  bool hasCxxInteroperability() const {
+    return Bits.ModuleDecl.HasCxxInteroperability;
+  }
+  void setHasCxxInteroperability(bool enabled = true) {
+    Bits.ModuleDecl.HasCxxInteroperability = enabled;
+  }
+
   /// \returns true if this module is a system module; note that the StdLib is
   /// considered a system module.
   bool isSystemModule() const {
diff --git a/include/swift/Basic/LangOptions.h b/include/swift/Basic/LangOptions.h
index 782803d85d6fc..8f77bc68ae512 100644
--- a/include/swift/Basic/LangOptions.h
+++ b/include/swift/Basic/LangOptions.h
@@ -313,6 +313,10 @@ namespace swift {
     /// Imports getters and setters as computed properties.
     bool CxxInteropGettersSettersAsProperties = false;
 
+    /// Should the compiler require C++ interoperability to be enabled
+    /// when importing Swift modules that enable C++ interoperability.
+    bool RequireCxxInteropToImportCxxInteropModule = true;
+
     /// On Darwin platforms, use the pre-stable ABI's mark bit for Swift
     /// classes instead of the stable ABI's bit. This is needed when
     /// targeting OSes prior to macOS 10.14.4 and iOS 12.2, where
diff --git a/include/swift/Option/FrontendOptions.td b/include/swift/Option/FrontendOptions.td
index df09e0f4ac622..8e8ed8d5b46bb 100644
--- a/include/swift/Option/FrontendOptions.td
+++ b/include/swift/Option/FrontendOptions.td
@@ -865,6 +865,11 @@ def cxx_interop_getters_setters_as_properties :
   HelpText<"Import getters and setters as computed properties in Swift">,
   Flags<[FrontendOption, HelpHidden]>;
 
+def cxx_interop_disable_requirement_at_import :
+  Flag<["-"], "disable-cxx-interop-requirement-at-import">,
+  HelpText<"Do not require C++ interoperability to be enabled when importing a Swift module that enables C++ interoperability">,
+  Flags<[FrontendOption, HelpHidden]>;
+
 def use_malloc : Flag<["-"], "use-malloc">,
   HelpText<"Allocate internal data structures using malloc "
            "(for memory debugging)">;
diff --git a/include/swift/Serialization/Validation.h b/include/swift/Serialization/Validation.h
index b2404b8516579..a82380e74963a 100644
--- a/include/swift/Serialization/Validation.h
+++ b/include/swift/Serialization/Validation.h
@@ -131,6 +131,7 @@ class ExtendedValidationInfo {
     unsigned IsBuiltFromInterface : 1;
     unsigned IsAllowModuleWithCompilerErrorsEnabled : 1;
     unsigned IsConcurrencyChecked : 1;
+    unsigned HasCxxInteroperability : 1;
   } Bits;
 public:
   ExtendedValidationInfo() : Bits() {}
@@ -232,6 +233,10 @@ class ExtendedValidationInfo {
   void setIsConcurrencyChecked(bool val = true) {
     Bits.IsConcurrencyChecked = val;
   }
+  bool hasCxxInteroperability() const { return Bits.HasCxxInteroperability; }
+  void setHasCxxInteroperability(bool val) {
+    Bits.HasCxxInteroperability = val;
+  }
 };
 
 struct SearchPath {
diff --git a/lib/AST/Module.cpp b/lib/AST/Module.cpp
index 0c695de33dfba..dd8a02dcb3f1b 100644
--- a/lib/AST/Module.cpp
+++ b/lib/AST/Module.cpp
@@ -646,6 +646,7 @@ ModuleDecl::ModuleDecl(Identifier name, ASTContext &ctx,
   Bits.ModuleDecl.HasHermeticSealAtLink = 0;
   Bits.ModuleDecl.IsConcurrencyChecked = 0;
   Bits.ModuleDecl.ObjCNameLookupCachePopulated = 0;
+  Bits.ModuleDecl.HasCxxInteroperability = 0;
 }
 
 void ModuleDecl::setIsSystemModule(bool flag) {
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 6849bc3f8e690..c75d5a467a4bd 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -1043,6 +1043,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
       Args.hasArg(OPT_experimental_c_foreign_reference_types);
 
   Opts.CxxInteropGettersSettersAsProperties = Args.hasArg(OPT_cxx_interop_getters_setters_as_properties);
+  Opts.RequireCxxInteropToImportCxxInteropModule =
+      !Args.hasArg(OPT_cxx_interop_disable_requirement_at_import);
 
   Opts.VerifyAllSubstitutionMaps |= Args.hasArg(OPT_verify_all_substitution_maps);
 
diff --git a/lib/Frontend/Frontend.cpp b/lib/Frontend/Frontend.cpp
index b4ff90136cf24..461c34938b15c 100644
--- a/lib/Frontend/Frontend.cpp
+++ b/lib/Frontend/Frontend.cpp
@@ -1319,6 +1319,9 @@ ModuleDecl *CompilerInstance::getMainModule() const {
       MainModule->setResilienceStrategy(ResilienceStrategy::Resilient);
     if (Invocation.getLangOptions().isSwiftVersionAtLeast(6))
       MainModule->setIsConcurrencyChecked(true);
+    if (Invocation.getLangOptions().EnableCXXInterop &&
+        Invocation.getLangOptions().RequireCxxInteropToImportCxxInteropModule)
+      MainModule->setHasCxxInteroperability();
 
     // Register the main module with the AST context.
     Context->addLoadedModule(MainModule);
diff --git a/lib/Serialization/ModuleFile.h b/lib/Serialization/ModuleFile.h
index 919f0f577e162..158b4f5edd0d6 100644
--- a/lib/Serialization/ModuleFile.h
+++ b/lib/Serialization/ModuleFile.h
@@ -621,6 +621,11 @@ class ModuleFile
     return Core->Bits.HasHermeticSealAtLink;
   }
 
+  /// Whether this module was built with C++ interoperability enabled.
+  bool hasCxxInteroperability() const {
+    return Core->Bits.HasCxxInteroperability;
+  }
+
   /// Whether the module is resilient. ('-enable-library-evolution')
   ResilienceStrategy getResilienceStrategy() const {
     return ResilienceStrategy(Core->Bits.ResilienceStrategy);
diff --git a/lib/Serialization/ModuleFileSharedCore.cpp b/lib/Serialization/ModuleFileSharedCore.cpp
index a96dea3cd0106..d4c325e22c6ea 100644
--- a/lib/Serialization/ModuleFileSharedCore.cpp
+++ b/lib/Serialization/ModuleFileSharedCore.cpp
@@ -181,6 +181,9 @@ static bool readOptionsBlock(llvm::BitstreamCursor &cursor,
     case options_block::MODULE_EXPORT_AS_NAME:
       extendedInfo.setExportAsName(blobData);
       break;
+    case options_block::HAS_CXX_INTEROPERABILITY_ENABLED:
+      extendedInfo.setHasCxxInteroperability(true);
+      break;
     default:
       // Unknown options record, possibly for use by a future version of the
       // module format.
@@ -1378,6 +1381,7 @@ ModuleFileSharedCore::ModuleFileSharedCore(
       Bits.IsAllowModuleWithCompilerErrorsEnabled =
           extInfo.isAllowModuleWithCompilerErrorsEnabled();
       Bits.IsConcurrencyChecked = extInfo.isConcurrencyChecked();
+      Bits.HasCxxInteroperability = extInfo.hasCxxInteroperability();
       MiscVersion = info.miscVersion;
       ModuleABIName = extInfo.getModuleABIName();
       ModulePackageName = extInfo.getModulePackageName();
diff --git a/lib/Serialization/ModuleFileSharedCore.h b/lib/Serialization/ModuleFileSharedCore.h
index 9ffdd6138a25a..13824c66a3407 100644
--- a/lib/Serialization/ModuleFileSharedCore.h
+++ b/lib/Serialization/ModuleFileSharedCore.h
@@ -386,8 +386,11 @@ class ModuleFileSharedCore {
     /// \c true if this module was built with complete checking for concurrency.
     unsigned IsConcurrencyChecked: 1;
 
+    /// Whether this module is built with C++ interoperability enabled.
+    unsigned HasCxxInteroperability : 1;
+
     // Explicitly pad out to the next word boundary.
-    unsigned : 4;
+    unsigned : 3;
   } Bits = {};
   static_assert(sizeof(ModuleBits) <= 8, "The bit set should be small");
 
diff --git a/lib/Serialization/ModuleFormat.h b/lib/Serialization/ModuleFormat.h
index e2f871b82df3f..885790790ccd7 100644
--- a/lib/Serialization/ModuleFormat.h
+++ b/lib/Serialization/ModuleFormat.h
@@ -58,7 +58,7 @@ const uint16_t SWIFTMODULE_VERSION_MAJOR = 0;
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
 /// Don't worry about adhering to the 80-column limit for this line.
-const uint16_t SWIFTMODULE_VERSION_MINOR = 790; // add `out` kind to mark uninitialized instruction
+const uint16_t SWIFTMODULE_VERSION_MINOR = 791; // HasCxxInteroperability
 
 /// A standard hash seed used for all string hashes in a serialized module.
 ///
@@ -888,6 +888,7 @@ namespace options_block {
     EXTERNAL_SEARCH_PLUGIN_PATH,
     COMPILER_PLUGIN_LIBRARY_PATH,
     COMPILER_PLUGIN_EXECUTABLE_PATH,
+    HAS_CXX_INTEROPERABILITY_ENABLED,
   };
 
   using SDKPathLayout = BCRecordLayout<
@@ -976,6 +977,10 @@ namespace options_block {
     MODULE_EXPORT_AS_NAME,
     BCBlob
   >;
+
+  using HasCxxInteroperabilityEnabledLayout = BCRecordLayout<
+    HAS_CXX_INTEROPERABILITY_ENABLED
+  >;
 }
 
 /// The record types within the input block.
diff --git a/lib/Serialization/Serialization.cpp b/lib/Serialization/Serialization.cpp
index 02bc669075a96..8f1758049b6cb 100644
--- a/lib/Serialization/Serialization.cpp
+++ b/lib/Serialization/Serialization.cpp
@@ -843,6 +843,7 @@ void Serializer::writeBlockInfoBlock() {
   BLOCK_RECORD(options_block, IS_ALLOW_MODULE_WITH_COMPILER_ERRORS_ENABLED);
   BLOCK_RECORD(options_block, MODULE_ABI_NAME);
   BLOCK_RECORD(options_block, IS_CONCURRENCY_CHECKED);
+  BLOCK_RECORD(options_block, HAS_CXX_INTEROPERABILITY_ENABLED);
   BLOCK_RECORD(options_block, MODULE_PACKAGE_NAME);
   BLOCK_RECORD(options_block, MODULE_EXPORT_AS_NAME);
   BLOCK_RECORD(options_block, PLUGIN_SEARCH_PATH);
@@ -1090,6 +1091,12 @@ void Serializer::writeHeader(const SerializationOptions &options) {
         IsConcurrencyChecked.emit(ScratchRecord);
       }
 
+      if (M->hasCxxInteroperability()) {
+        options_block::HasCxxInteroperabilityEnabledLayout
+            CxxInteroperabilityEnabled(Out);
+        CxxInteroperabilityEnabled.emit(ScratchRecord);
+      }
+
       if (options.SerializeOptionsForDebugging) {
         options_block::SDKPathLayout SDKPath(Out);
         options_block::XCCLayout XCC(Out);
diff --git a/lib/Serialization/SerializedModuleLoader.cpp b/lib/Serialization/SerializedModuleLoader.cpp
index 03984e311e507..6b952b96295ae 100644
--- a/lib/Serialization/SerializedModuleLoader.cpp
+++ b/lib/Serialization/SerializedModuleLoader.cpp
@@ -824,6 +824,8 @@ LoadedFile *SerializedModuleLoaderBase::loadAST(
       M.setABIName(Ctx.getIdentifier(loadedModuleFile->getModuleABIName()));
     if (loadedModuleFile->isConcurrencyChecked())
       M.setIsConcurrencyChecked();
+    if (loadedModuleFile->hasCxxInteroperability())
+      M.setHasCxxInteroperability();
     if (!loadedModuleFile->getModulePackageName().empty()) {
       M.setPackageName(Ctx.getIdentifier(loadedModuleFile->getModulePackageName()));
     }
@@ -896,6 +898,19 @@ LoadedFile *SerializedModuleLoaderBase::loadAST(
                        diag::need_hermetic_seal_to_import_module, M.getName());
   }
 
+  // Non-resilient modules built with C++ interoperability enabled
+  // are typically incompatible with clients that do not enable
+  // C++ interoperability.
+  if (M.hasCxxInteroperability() &&
+      M.getResilienceStrategy() != ResilienceStrategy::Resilient &&
+      !Ctx.LangOpts.EnableCXXInterop &&
+      Ctx.LangOpts.RequireCxxInteropToImportCxxInteropModule) {
+    auto loc = diagLoc.value_or(SourceLoc());
+    Ctx.Diags.diagnose(loc, diag::need_cxx_interop_to_import_module,
+                       M.getName());
+    Ctx.Diags.diagnose(loc, diag::enable_cxx_interop_docs);
+  }
+
   return fileUnit;
 }
 
diff --git a/test/Interop/Cxx/implementation-only-imports/import-implementation-only-cxx-interop-module-without-interop.swift b/test/Interop/Cxx/implementation-only-imports/import-implementation-only-cxx-interop-module-without-interop.swift
index ecb08c10d0641..1f8a69da51a32 100644
--- a/test/Interop/Cxx/implementation-only-imports/import-implementation-only-cxx-interop-module-without-interop.swift
+++ b/test/Interop/Cxx/implementation-only-imports/import-implementation-only-cxx-interop-module-without-interop.swift
@@ -1,11 +1,11 @@
 // RUN: %empty-directory(%t)
 
-// RUN: %target-swift-frontend %S/Inputs/use-module-a-impl-only.swift -I %S/Inputs/ -module-name UseModuleAImplOnly -emit-module -emit-module-path %t/UseModuleAImplOnly.swiftmodule -cxx-interoperability-mode=default
+// RUN: %target-swift-frontend %S/Inputs/use-module-a-impl-only.swift -I %S/Inputs/ -module-name UseModuleAImplOnly -emit-module -emit-module-path %t/UseModuleAImplOnly.swiftmodule -cxx-interoperability-mode=default -enable-library-evolution
 
 // RUN: %target-swift-frontend %s -typecheck -module-name TestMod -I %t -I %S/Inputs
 
 // Check that we have used something from CxxShim in 'UseModuleAImplOnly'
-// RUN: %target-swift-frontend %S/Inputs/use-module-a-impl-only.swift -I %S/Inputs/ -module-name UseModuleAImplOnly -emit-module -emit-module-path %t/UseModuleAImplOnly.swiftmodule -cxx-interoperability-mode=default -emit-sil -o - | %FileCheck %s
+// RUN: %target-swift-frontend %S/Inputs/use-module-a-impl-only.swift -I %S/Inputs/ -module-name UseModuleAImplOnly -emit-module -emit-module-path %t/UseModuleAImplOnly.swiftmodule -cxx-interoperability-mode=default -emit-sil -o - -enable-library-evolution | %FileCheck %s
 // CHECK: __swift_interopStaticCast
 
 import UseModuleAImplOnly
diff --git a/test/Interop/Cxx/implementation-only-imports/import-implementation-only-cxxstdlib-interop-module-without-interop.swift b/test/Interop/Cxx/implementation-only-imports/import-implementation-only-cxxstdlib-interop-module-without-interop.swift
index 430fce25bbbf7..f020d6c941dec 100644
--- a/test/Interop/Cxx/implementation-only-imports/import-implementation-only-cxxstdlib-interop-module-without-interop.swift
+++ b/test/Interop/Cxx/implementation-only-imports/import-implementation-only-cxxstdlib-interop-module-without-interop.swift
@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 
-// RUN: %target-swift-frontend %S/Inputs/use-cxx-stdlib-impl-only.swift -I %S/Inputs/ -module-name UseCxxStdlibImplOnly -emit-module -emit-module-path %t/UseCxxStdlibImplOnly.swiftmodule -cxx-interoperability-mode=default
+// RUN: %target-swift-frontend %S/Inputs/use-cxx-stdlib-impl-only.swift -I %S/Inputs/ -module-name UseCxxStdlibImplOnly -emit-module -emit-module-path %t/UseCxxStdlibImplOnly.swiftmodule -cxx-interoperability-mode=default -enable-library-evolution
 
 // RUN: %target-swift-frontend %s -typecheck -module-name TestMod -I %t -I %S/Inputs
 
diff --git a/test/Interop/Cxx/modules/prohibit-import-into-non-interop-compilation.swift b/test/Interop/Cxx/modules/prohibit-import-into-non-interop-compilation.swift
new file mode 100644
index 0000000000000..ce36822467f41
--- /dev/null
+++ b/test/Interop/Cxx/modules/prohibit-import-into-non-interop-compilation.swift
@@ -0,0 +1,21 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend %s -module-name UsesCxxInterop -emit-module -emit-module-path %t/UsesCxxInterop.swiftmodule -cxx-interoperability-mode=default
+
+// RUN: %target-swift-frontend %s -D USE -typecheck -module-name TestMod -I %t -verify
+
+// RUN: %target-swift-frontend %s -D USE -typecheck -module-name TestMod -I %t -disable-cxx-interop-requirement-at-import
+
+// Verify that 'disable-cxx-interop-requirement-at-import' works for the module being built.
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %s -module-name UsesCxxInterop -emit-module -emit-module-path %t/UsesCxxInterop.swiftmodule -cxx-interoperability-mode=default -disable-cxx-interop-requirement-at-import
+// RUN: %target-swift-frontend %s -D USE -typecheck -module-name TestMod -I %t
+
+#if USE
+import UsesCxxInterop // expected-error {{module 'UsesCxxInterop' was built with C++ interoperability enabled, but current compilation does not enable C++ interoperability}}
+// expected-note@-1 {{visit https://www.swift.org/documentation/cxx-interop/project-build-setup to learn how to enable C++ interoperability}}
+
+#else
+public func testFun() { }
+
+#endif