diff --git a/include/clang/Frontend/PreprocessorOptions.h b/include/clang/Frontend/PreprocessorOptions.h
index 30a3406..0ee8cb3 100644
--- a/include/clang/Frontend/PreprocessorOptions.h
+++ b/include/clang/Frontend/PreprocessorOptions.h
@@ -206,7 +206,6 @@
   /// \brief Reset any options that are not considered when building a
   /// module.
   void resetNonModularOptions() {
-    Macros.clear();
     Includes.clear();
     MacroIncludes.clear();
     ChainedIncludes.clear();
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 5358106..1debf3b 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -2026,6 +2026,23 @@
   Signature.add(getPreprocessorOpts().UsePredefines, 1);
   Signature.add(getPreprocessorOpts().DetailedRecord, 1);
   
+  // Hash the preprocessor defines.
+  // FIXME: This is terrible. Use an MD5 sum of the preprocessor defines.
+  std::vector<StringRef> MacroDefs;
+  for (std::vector<std::pair<std::string, bool/*isUndef*/> >::const_iterator 
+            I = getPreprocessorOpts().Macros.begin(),
+         IEnd = getPreprocessorOpts().Macros.end();
+       I != IEnd; ++I) {
+    if (!I->second)
+      MacroDefs.push_back(I->first);
+  }
+  llvm::array_pod_sort(MacroDefs.begin(), MacroDefs.end());
+       
+  unsigned PPHashResult = 0;
+  for (unsigned I = 0, N = MacroDefs.size(); I != N; ++I)
+    PPHashResult = llvm::HashString(MacroDefs[I], PPHashResult);
+  Signature.add(PPHashResult, 32);
+  
   // We've generated the signature. Treat it as one large APInt that we'll
   // encode in base-36 and return.
   Signature.flush();
diff --git a/test/Modules/Inputs/CmdLine.framework/Headers/CmdLine.h b/test/Modules/Inputs/CmdLine.framework/Headers/CmdLine.h
new file mode 100644
index 0000000..46b8fc0
--- /dev/null
+++ b/test/Modules/Inputs/CmdLine.framework/Headers/CmdLine.h
@@ -0,0 +1,6 @@
+#ifdef FOO_RETURNS_INT_PTR
+int *foo(void);
+#else
+float *foo(void);
+#endif
+
diff --git a/test/Modules/on-demand-build-warnings.m b/test/Modules/on-demand-build-warnings.m
index ea53169..aa122db 100644
--- a/test/Modules/on-demand-build-warnings.m
+++ b/test/Modules/on-demand-build-warnings.m
@@ -1,5 +1,5 @@
 // RUN: rm -rf %t
-// RUN: %clang_cc1 -fno-objc-infer-related-result-type -Wmodule-build -fmodule-cache-path %t -F %S/Inputs -DFOO -verify %s
+// RUN: %clang_cc1 -fno-objc-infer-related-result-type -Wmodule-build -fmodule-cache-path %t -F %S/Inputs -verify %s
 
 __import_module__ Module; // expected-warning{{building module 'Module' from source}}
 
diff --git a/test/Modules/on-demand-build.m b/test/Modules/on-demand-build.m
index 418e912..649caa8 100644
--- a/test/Modules/on-demand-build.m
+++ b/test/Modules/on-demand-build.m
@@ -1,8 +1,8 @@
 // RUN: rm -rf %t
-// RUN: %clang_cc1 -fno-objc-infer-related-result-type -Werror -fmodule-cache-path %t -F %S/Inputs -DFOO -verify %s
-// RUN: %clang_cc1 -fno-objc-infer-related-result-type -Werror -x objective-c++ -fmodule-cache-path %t -F %S/Inputs -DFOO -verify %s
-// RUN: %clang_cc1 -fno-objc-infer-related-result-type -Werror -fmodule-cache-path %t -F %S/Inputs -DFOO -verify %s
-
+// RUN: %clang_cc1 -fno-objc-infer-related-result-type -Werror -fmodule-cache-path %t -F %S/Inputs -verify %s
+// RUN: %clang_cc1 -fno-objc-infer-related-result-type -Werror -x objective-c++ -fmodule-cache-path %t -F %S/Inputs -verify %s
+// RUN: %clang_cc1 -fno-objc-infer-related-result-type -Werror -fmodule-cache-path %t -F %S/Inputs -verify %s
+#define FOO
 __import_module__ Module;
 @interface OtherClass
 @end
diff --git a/test/Modules/on-demand-macros.m b/test/Modules/on-demand-macros.m
new file mode 100644
index 0000000..96abb23
--- /dev/null
+++ b/test/Modules/on-demand-macros.m
@@ -0,0 +1,13 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -fmodule-cache-path %t -F %S/Inputs -DFOO_RETURNS_INT_PTR -verify %s
+// RUN: %clang_cc1 -fmodule-cache-path %t -F %S/Inputs -verify %s
+
+__import_module__ CmdLine;
+
+void test() {
+#ifdef FOO_RETURNS_INT_PTR
+  int *ip = foo();
+#else
+  float *fp = foo();
+#endif
+}