diff --git a/src/indexer.cc b/src/indexer.cc
index 1683a55b..7cc19b04 100644
--- a/src/indexer.cc
+++ b/src/indexer.cc
@@ -257,6 +257,8 @@ std::string GetDocumentContentInRange(CXTranslationUnit cx_tu, CXSourceRange ran
 
 
 
+// static
+int IndexFile::kCurrentVersion = 4;
 
 IndexFile::IndexFile(const std::string& path) : id_cache(path), path(path) {
   // TODO: Reconsider if we should still be reusing the same id_cache.
diff --git a/src/indexer.h b/src/indexer.h
index 235dd887..58342d1e 100644
--- a/src/indexer.h
+++ b/src/indexer.h
@@ -455,7 +455,7 @@ MAKE_REFLECT_STRUCT(IndexInclude, line, resolved_path);
 struct IndexFile {
   IdCache id_cache;
 
-  static constexpr int kCurrentVersion = 4;
+  static int kCurrentVersion;
   int version = 0;
 
   std::string path;