Index: include/clang/Basic/Sanitizers.h
===================================================================
--- include/clang/Basic/Sanitizers.h
+++ include/clang/Basic/Sanitizers.h
@@ -61,8 +61,9 @@
     Mask = Value ? (Mask | K) : (Mask & ~K);
   }
 
-  /// \brief Disable all sanitizers.
-  void clear() { Mask = 0; }
+  /// \brief Disable the sanitizers specified in \p K (by default, disable
+  /// all sanitizers).
+  void clear(SanitizerMask K = SanitizerKind::All) { Mask &= ~K; }
 
   /// \brief Returns true if at least one sanitizer is enabled.
   bool empty() const { return Mask == 0; }
@@ -79,6 +80,13 @@
 /// this group enables.
 SanitizerMask expandSanitizerGroups(SanitizerMask Kinds);
 
+/// Return the sanitizers which, when enabled, cannot affect preprocessing or
+/// AST generation.
+static inline SanitizerMask getModularSanitizers() {
+  return SanitizerKind::CFI | SanitizerKind::Integer |
+         SanitizerKind::Nullability | SanitizerKind::Undefined;
+}
+
 }  // end namespace clang
 
 #endif
Index: lib/Basic/LangOptions.cpp
===================================================================
--- lib/Basic/LangOptions.cpp
+++ lib/Basic/LangOptions.cpp
@@ -29,9 +29,7 @@
   Name = Default;
 #include "clang/Basic/LangOptions.def"
 
-  // FIXME: This should not be reset; modules can be different with different
-  // sanitizer options (this affects __has_feature(address_sanitizer) etc).
-  Sanitize.clear();
+  // These options do not affect AST generation.
   SanitizerBlacklistFiles.clear();
   XRayAlwaysInstrumentFiles.clear();
   XRayNeverInstrumentFiles.clear();
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -2693,6 +2693,13 @@
     code = ext->hashExtension(code);
   }
 
+  // Extend the signature with the enabled sanitizers, if at least one is
+  // enabled. Sanitizers which cannot affect AST generation aren't hashed.
+  SanitizerSet SanHash = LangOpts->Sanitize;
+  SanHash.clear(getModularSanitizers());
+  if (!SanHash.empty())
+    code = hash_combine(code, SanHash.Mask);
+
   return llvm::APInt(64, code).toString(36, /*Signed=*/false);
 }
 
Index: lib/Serialization/ASTReader.cpp
===================================================================
--- lib/Serialization/ASTReader.cpp
+++ lib/Serialization/ASTReader.cpp
@@ -292,6 +292,33 @@
     return true;
   }
 
+  // Sanitizer feature mismatches are treated as compatible differences. If
+  // compatible differences aren't allowed, we still only want to check for
+  // mismatches of non-modular sanitizers (the only ones which can affect AST
+  // generation).
+  if (!AllowCompatibleDifferences) {
+    SanitizerMask ModularSanitizers = getModularSanitizers();
+    SanitizerSet ExistingSanitizers = ExistingLangOpts.Sanitize;
+    SanitizerSet ImportedSanitizers = LangOpts.Sanitize;
+    ExistingSanitizers.clear(ModularSanitizers);
+    ImportedSanitizers.clear(ModularSanitizers);
+    if (ExistingSanitizers.Mask != ImportedSanitizers.Mask) {
+      const std::string Flag = "-fsanitize=";
+      if (Diags) {
+#define SANITIZER(NAME, ID)                                                    \
+  {                                                                            \
+    bool InExistingModule = ExistingSanitizers.has(SanitizerKind::ID);         \
+    bool InImportedModule = ImportedSanitizers.has(SanitizerKind::ID);         \
+    if (InExistingModule != InImportedModule)                                  \
+      Diags->Report(diag::err_pch_targetopt_feature_mismatch)                  \
+          << InExistingModule << (Flag + NAME);                                \
+  }
+#include "clang/Basic/Sanitizers.def"
+      }
+      return true;
+    }
+  }
+
   return false;
 }
 
Index: test/Modules/Inputs/check-for-sanitizer-feature/check.h
===================================================================
--- /dev/null
+++ test/Modules/Inputs/check-for-sanitizer-feature/check.h
@@ -0,0 +1,5 @@
+#if __has_feature(address_sanitizer)
+#define HAS_ASAN 1
+#else
+#define HAS_ASAN 0
+#endif
Index: test/Modules/Inputs/check-for-sanitizer-feature/map
===================================================================
--- /dev/null
+++ test/Modules/Inputs/check-for-sanitizer-feature/map
@@ -0,0 +1,3 @@
+module check_feature {
+  header "check.h"
+}
Index: test/Modules/check-for-sanitizer-feature.cpp
===================================================================
--- /dev/null
+++ test/Modules/check-for-sanitizer-feature.cpp
@@ -0,0 +1,66 @@
+// RUN: rm -rf %t.1 %t.2
+// RUN: mkdir %t.1 %t.2
+
+// Build and use an ASan-enabled module.
+// RUN: %clang_cc1 -fsanitize=address -fmodules -fmodules-cache-path=%t.1 \
+// RUN:   -fmodule-map-file=%S/Inputs/check-for-sanitizer-feature/map \
+// RUN:   -I %S/Inputs/check-for-sanitizer-feature -verify %s
+// RUN: ls %t.1 | count 2
+
+// Force a module rebuild by disabling ASan.
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t.1 \
+// RUN:   -fmodule-map-file=%S/Inputs/check-for-sanitizer-feature/map \
+// RUN:   -I %S/Inputs/check-for-sanitizer-feature -verify %s
+// RUN: ls %t.1 | count 3
+
+// Enable ASan again: check that there is no import failure, and no rebuild.
+// RUN: %clang_cc1 -fsanitize=address -fmodules -fmodules-cache-path=%t.1 \
+// RUN:   -fmodule-map-file=%S/Inputs/check-for-sanitizer-feature/map \
+// RUN:   -I %S/Inputs/check-for-sanitizer-feature -verify %s
+// RUN: ls %t.1 | count 3
+
+// Some sanitizers can not affect AST generation when enabled. Check that
+// module rebuilds don't occur when these sanitizers are enabled.
+//
+// First, build without any sanitization.
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t.2 \
+// RUN:   -fmodule-map-file=%S/Inputs/check-for-sanitizer-feature/map \
+// RUN:   -I %S/Inputs/check-for-sanitizer-feature -verify %s
+// RUN: ls %t.2 | count 2
+//
+// Next, build with sanitization, and check that a new module isn't built.
+// RUN: %clang_cc1 -fsanitize=cfi-vcall,unsigned-integer-overflow,nullability-arg,null -fmodules \
+// RUN:   -fmodules-cache-path=%t.2 \
+// RUN:   -fmodule-map-file=%S/Inputs/check-for-sanitizer-feature/map \
+// RUN:   -I %S/Inputs/check-for-sanitizer-feature -verify %s
+// RUN: ls %t.2 | count 2
+
+// Finally, test that including enabled sanitizers in the module hash isn't
+// required to ensure correctness of module imports.
+//
+// Emit a PCH with ASan enabled.
+// RUN: %clang_cc1 -x c -fsanitize=address %S/Inputs/check-for-sanitizer-feature/check.h -emit-pch -o %t.asan_pch
+//
+// Import the PCH without ASan enabled (we expect an error).
+// RUN: not %clang_cc1 -x c -include-pch %t.asan_pch %s -verify 2>&1 | FileCheck %s --check-prefix=PCH_MISMATCH
+// PCH_MISMATCH: AST file was compiled with the target feature'-fsanitize=address' but the current translation unit is not
+//
+// Emit a PCH with UBSan enabled.
+// RUN: %clang_cc1 -x c -fsanitize=null %S/Inputs/check-for-sanitizer-feature/check.h -emit-pch -o %t.ubsan_pch
+//
+// Import the PCH without UBSan enabled (should work just fine).
+// RUN: %clang_cc1 -x c -include-pch %t.ubsan_pch %s -I %S/Inputs/check-for-sanitizer-feature -verify
+
+#include "check.h"
+
+#if __has_feature(address_sanitizer)
+#if HAS_ASAN != 1
+#error Module doesn't have the address_sanitizer feature, but main program does.
+#endif
+#else
+#if HAS_ASAN != 0
+#error Module has the address_sanitizer feature, but main program doesn't.
+#endif
+#endif
+
+// expected-no-diagnostics