diff --git a/tools/js_optimizer.py b/tools/js_optimizer.py
index ad18935e2..82545653a 100644
--- a/tools/js_optimizer.py
+++ b/tools/js_optimizer.py
@@ -43,7 +43,6 @@ def get_native_optimizer():
         for compiler in [shared.CLANG, 'g++', 'clang++']: # try our clang first, otherwise hope for a system compiler in the path
           shared.logging.debug('  using ' + compiler)
           out, err = subprocess.Popen([compiler,
-                                       shared.path_from_root('tools', 'optimizer', 'istring.cpp'),
                                        shared.path_from_root('tools', 'optimizer', 'parser.cpp'),
                                        shared.path_from_root('tools', 'optimizer', 'simple_ast.cpp'),
                                        shared.path_from_root('tools', 'optimizer', 'optimizer.cpp'),
diff --git a/tools/optimizer/istring.cpp b/tools/optimizer/istring.cpp
deleted file mode 100644
index cb81dba6b..000000000
--- a/tools/optimizer/istring.cpp
+++ /dev/null
@@ -1,8 +0,0 @@
-#include "istring.h"
-
-namespace cashew {
-
-IString::StringSet IString::strings;
-
-} // namespace cashew
-
diff --git a/tools/optimizer/istring.h b/tools/optimizer/istring.h
index 281db08e1..d8cd3cc5e 100644
--- a/tools/optimizer/istring.h
+++ b/tools/optimizer/istring.h
@@ -35,8 +35,6 @@ struct IString {
       return strcmp(x, y) == 0;
     }
   };
-  typedef std::unordered_set<const char *, CStringHash, CStringEqual> StringSet;
-  static StringSet strings;
 
   IString() : str(nullptr) {}
   IString(const char *s, bool reuse=true) { // if reuse=true, then input is assumed to remain alive; not copied
@@ -44,19 +42,22 @@ struct IString {
   }
 
   void set(const char *s, bool reuse=true) {
+    typedef std::unordered_set<const char *, CStringHash, CStringEqual> StringSet;
+    static StringSet* strings = new StringSet();
+
     if (reuse) {
-      auto result = strings.insert(s); // if already present, does nothing
+      auto result = strings->insert(s); // if already present, does nothing
       str = *(result.first);
     } else {
-      auto existing = strings.find(s);
-      if (existing == strings.end()) {
+      auto existing = strings->find(s);
+      if (existing == strings->end()) {
         char *copy = (char*)malloc(strlen(s)+1); // XXX leaked
         strcpy(copy, s);
         s = copy;
       } else {
         s = *existing;
       }
-      strings.insert(s);
+      strings->insert(s);
       str = s;
     }
   }