diff --git a/indra/llmath/llcalcparser.h b/indra/llmath/llcalcparser.h
index e6298b7e74..73bc05a867 100644
--- a/indra/llmath/llcalcparser.h
+++ b/indra/llmath/llcalcparser.h
@@ -27,7 +27,7 @@
 #ifndef LL_CALCPARSER_H
 #define LL_CALCPARSER_H
 
-#define BOOST_SPIRIT_SINGLE_GRAMMAR_INSTANCE
+#define BOOST_SPIRIT_THREADSAFE
 
 #include <boost/spirit/include/classic_attribute.hpp>
 #include <boost/spirit/include/classic_core.hpp>
diff --git a/indra/newview/fslslpreproc.cpp b/indra/newview/fslslpreproc.cpp
index b64da3fd69..e67e90ebb3 100644
--- a/indra/newview/fslslpreproc.cpp
+++ b/indra/newview/fslslpreproc.cpp
@@ -110,7 +110,7 @@ std::map<std::string,LLUUID> FSLSLPreprocessor::cached_assetids;
 #ifdef LL_WINDOWS
 #pragma warning (disable : 4702) // warning C4702: unreachable code
 #endif
-#define BOOST_SPIRIT_SINGLE_GRAMMAR_INSTANCE
+//#define BOOST_SPIRIT_THREADSAFE
 
 #include <boost/assert.hpp>
 #include <boost/wave.hpp>