diff --git a/js/src/jsfun.cpp b/js/src/jsfun.cpp
index 4b681dafa64..44cb1086951 100644
--- a/js/src/jsfun.cpp
+++ b/js/src/jsfun.cpp
@@ -471,7 +471,9 @@ WrapEscapingClosure(JSContext *cx, JSStackFrame *fp, JSObject *funobj, JSFunctio
      * Fill in the rest of wscript. This means if you add members to JSScript
      * you must update this code. FIXME: factor into JSScript::clone method.
      */
-    wscript->flags = script->flags;
+    wscript->noScriptRval = script->noScriptRval;
+    wscript->savedCallerFun = script->savedCallerFun;
+    wscript->hasSharps = script->hasSharps;
     wscript->version = script->version;
     wscript->nfixed = script->nfixed;
     wscript->filename = script->filename;
diff --git a/js/src/jsinterp.cpp b/js/src/jsinterp.cpp
index 940507a51ba..2e922751d3e 100644
--- a/js/src/jsinterp.cpp
+++ b/js/src/jsinterp.cpp
@@ -1523,11 +1523,11 @@ js_Execute(JSContext *cx, JSObject *chain, JSScript *script,
 #if JS_HAS_SHARP_VARS
         JS_STATIC_ASSERT(SHARP_NSLOTS == 2);
 
-        if (script->flags & JSSF_HAS_SHARPS) {
+        if (script->hasSharps) {
             JS_ASSERT(script->nfixed >= SHARP_NSLOTS);
             jsval *sharps = &frame.slots[script->nfixed - SHARP_NSLOTS];
 
-            if (down && down->script && (down->script->flags & JSSF_HAS_SHARPS)) {
+            if (down && down->script && down->script->hasSharps) {
                 JS_ASSERT(down->script->nfixed >= SHARP_NSLOTS);
                 int base = (down->fun && !(down->flags & JSFRAME_SPECIAL))
                            ? down->fun->sharpSlotBase(cx)
diff --git a/js/src/jsobj.cpp b/js/src/jsobj.cpp
index b30964eebe7..7d518fdb404 100644
--- a/js/src/jsobj.cpp
+++ b/js/src/jsobj.cpp
@@ -1419,7 +1419,7 @@ obj_eval(JSContext *cx, JSObject *obj, uintN argc, jsval *argv, jsval *rval)
 
         EVAL_CACHE_METER(probe);
         while ((script = *scriptp) != NULL) {
-            if ((script->flags & JSSF_SAVED_CALLER_FUN) &&
+            if (script->savedCallerFun &&
                 script->version == cx->version &&
                 (script->principals == principals ||
                  (principals->subsume(principals, script->principals) &&
diff --git a/js/src/jsopcode.cpp b/js/src/jsopcode.cpp
index 54cfbd38f34..9f5ee889168 100644
--- a/js/src/jsopcode.cpp
+++ b/js/src/jsopcode.cpp
@@ -2816,7 +2816,7 @@ Decompile(SprintStack *ss, jsbytecode *pc, intN nb, JSOp nextop)
               case JSOP_CALLDSLOT:
               {
                 if (!jp->fun) {
-                    JS_ASSERT(jp->script->flags & JSSF_SAVED_CALLER_FUN);
+                    JS_ASSERT(jp->script->savedCallerFun);
                     jp->fun = jp->script->getFunction(0);
                 }
 
diff --git a/js/src/jsparse.cpp b/js/src/jsparse.cpp
index 4d23070759d..75149af66b9 100644
--- a/js/src/jsparse.cpp
+++ b/js/src/jsparse.cpp
@@ -1001,7 +1001,7 @@ JSCompiler::compileScript(JSContext *cx, JSObject *scopeChain, JSStackFrame *cal
 #endif
     script = js_NewScriptFromCG(cx, &cg);
     if (script && funbox)
-        script->flags |= JSSF_SAVED_CALLER_FUN;
+        script->savedCallerFun = true;
 
 #ifdef JS_SCOPE_DEPTH_METER
     if (script) {
diff --git a/js/src/jsscript.cpp b/js/src/jsscript.cpp
index fa0a11ec4c9..2176ff58013 100644
--- a/js/src/jsscript.cpp
+++ b/js/src/jsscript.cpp
@@ -1531,9 +1531,9 @@ js_NewScriptFromCG(JSContext *cx, JSCodeGenerator *cg)
     if (cg->regexpList.length != 0)
         cg->regexpList.finish(script->regexps());
     if (cg->flags & TCF_NO_SCRIPT_RVAL)
-        script->flags |= JSSF_NO_SCRIPT_RVAL;
+        script->noScriptRval = true;
     if (cg->hasSharps())
-        script->flags |= JSSF_HAS_SHARPS;
+        script->hasSharps = true;
 
     if (cg->upvarList.count != 0) {
         JS_ASSERT(cg->upvarList.count <= cg->upvarMap.length);
diff --git a/js/src/jsscript.h b/js/src/jsscript.h
index 62e46297b03..1d85fcb1476 100644
--- a/js/src/jsscript.h
+++ b/js/src/jsscript.h
@@ -115,7 +115,11 @@ struct JSScript {
                                        regexps or 0 if none. */
     uint8           trynotesOffset; /* offset to the array of try notes or
                                        0 if none */
-    uint8           flags;      /* see below */
+    bool            noScriptRval:1; /* no need for result value of last
+                                       expression statement */
+    bool            savedCallerFun:1; /* object 0 is caller function */
+    bool            hasSharps:1;      /* script uses sharp variables */
+
     jsbytecode      *main;      /* main entry point, after predef'ing prolog */
     JSAtomMap       atomMap;    /* maps immediate index to literal struct */
     const char      *filename;  /* source filename or null */
@@ -170,11 +174,6 @@ struct JSScript {
     inline JSObject *getRegExp(size_t index);
 };
 
-#define JSSF_NO_SCRIPT_RVAL     0x01    /* no need for result value of last
-                                           expression statement */
-#define JSSF_SAVED_CALLER_FUN   0x02    /* object 0 is caller function */
-#define JSSF_HAS_SHARPS         0x04    /* script uses sharp variables */
-
 #define SHARP_NSLOTS            2       /* [#array, #depth] slots if the script
                                            uses sharp variables */