diff --git a/sandboxed_api/tools/clang_generator/generator.h b/sandboxed_api/tools/clang_generator/generator.h
index 218981f..5cd118e 100644
--- a/sandboxed_api/tools/clang_generator/generator.h
+++ b/sandboxed_api/tools/clang_generator/generator.h
@@ -26,6 +26,7 @@
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/CompilerInvocation.h"
 #include "clang/Frontend/FrontendAction.h"
+#include "clang/Lex/Preprocessor.h"
 #include "clang/Tooling/Tooling.h"
 #include "sandboxed_api/tools/clang_generator/emitter.h"
 #include "sandboxed_api/tools/clang_generator/types.h"
@@ -116,6 +117,11 @@ class GeneratorAction : public clang::ASTFrontendAction {
                                                   emitter_, options_);
   }
 
+  bool BeginSourceFileAction(clang::CompilerInstance& ci) override {
+    ci.getPreprocessor().enableIncrementalProcessing();
+    return true;
+  }
+
   bool hasCodeCompletionSupport() const override { return false; }
 
   Emitter& emitter_;