diff --git a/src/per_expand_data.cc b/src/per_expand_data.cc
index f8f3025..0a468cf 100644
--- a/src/per_expand_data.cc
+++ b/src/per_expand_data.cc
@@ -42,10 +42,12 @@ namespace ctemplate {
 
 using std::string;
 
+#ifndef _MSC_VER
 bool PerExpandData::DataEq::operator()(const char* s1, const char* s2) const {
   return ((s1 == 0 && s2 == 0) ||
           (s1 && s2 && *s1 == *s2 && strcmp(s1, s2) == 0));
 }
+#endif
 
 PerExpandData::~PerExpandData() {
   delete map_;
