diff --git a/js/src/jsapi.c b/js/src/jsapi.c
index 1b6dd4172af0..84ffa0359ece 100644
--- a/js/src/jsapi.c
+++ b/js/src/jsapi.c
@@ -858,11 +858,6 @@ JS_SetVersion(JSContext *cx, JSVersion version)
     }
 #endif /* !JS_BUG_FALLIBLE_EQOPS */
 
-#if JS_HAS_EXPORT_IMPORT
-    /* XXX this might fail due to low memory */
-    js_InitScanner(cx);
-#endif /* JS_HAS_EXPORT_IMPORT */
-
     return oldVersion;
 }
 
diff --git a/js/src/jscntxt.h b/js/src/jscntxt.h
index b12e131ffc40..07939877077b 100644
--- a/js/src/jscntxt.h
+++ b/js/src/jscntxt.h
@@ -233,6 +233,9 @@ struct JSContext {
     jsval               exception;          /* most-recently-thrown exceptin */
 
     uint32              options;            /* see jsapi.h for JSOPTION_* */
+
+    /* Delay JS_SetVersion scanner effects until they're needed. */
+    JSVersion           scannerVersion;
 };
 
 /* Slightly more readable macros, also to hide bitset implementation detail. */
diff --git a/js/src/jsscan.c b/js/src/jsscan.c
index 1f85566f2ab6..cd98bb6dc40e 100644
--- a/js/src/jsscan.c
+++ b/js/src/jsscan.c
@@ -216,6 +216,12 @@ js_NewBufferTokenStream(JSContext *cx, const jschar *base, size_t length)
     size_t nb;
     JSTokenStream *ts;
 
+    if (cx->scannerVersion != cx->version) {
+        if (!js_InitScanner(cx))
+            return NULL;
+        cx->scannerVersion = cx->version;
+    }
+
     nb = sizeof(JSTokenStream) + JS_LINE_LIMIT * sizeof(jschar);
     JS_ARENA_ALLOCATE(ts, &cx->tempPool, nb);
     if (!ts) {
@@ -666,7 +672,7 @@ AddToTokenBuf(JSContext *cx, JSTokenBuf *tb, jschar c)
 * Otherwise, non-destructively return the original '\'.
 */
 static int32 
-getUnicodeEscape(JSTokenStream *ts)
+GetUnicodeEscape(JSTokenStream *ts)
 {
     jschar cp[5];
     int32 c;
@@ -733,23 +739,23 @@ retry:
 
     hadUnicodeEscape = JS_FALSE;
     if (JS_ISIDENT_START(c) ||
-        ((c == '\\') &&
-            (c = getUnicodeEscape(ts), 
-            hadUnicodeEscape = JS_ISIDENT_START(c)))) {
+        (c == '\\' &&
+         (c = GetUnicodeEscape(ts), 
+          hadUnicodeEscape = JS_ISIDENT_START(c)))) {
 	INIT_TOKENBUF(&ts->tokenbuf);
         for (;;) {
 	    if (!AddToTokenBuf(cx, &ts->tokenbuf, (jschar)c))
 		RETURN(TOK_ERROR);
 	    c = GetChar(ts);
             if (c == '\\') {
-                c = getUnicodeEscape(ts);
-                if (JS_ISIDENT(c))
-                    hadUnicodeEscape = JS_TRUE;
-                else
+                c = GetUnicodeEscape(ts);
+                if (!JS_ISIDENT(c))
+                    break;
+                hadUnicodeEscape = JS_TRUE;
+            } else {
+                if (!JS_ISIDENT(c))
                     break;
             }
-            else
-                if (!JS_ISIDENT(c)) break;
         }
 	UngetChar(ts, c);
 	FINISH_TOKENBUF(&ts->tokenbuf);
@@ -760,16 +766,13 @@ retry:
 			       0);
 	if (!atom)
 	    RETURN(TOK_ERROR);
-        if (hadUnicodeEscape) /* Can never be a keyword, then. */
-            atom->kwindex = -1;
-        else
-	    if (atom->kwindex >= 0) {
-	        struct keyword *kw;
+        if (!hadUnicodeEscape && atom->kwindex >= 0) {
+            struct keyword *kw;
 
-	        kw = &keywords[atom->kwindex];
-	        tp->t_op = (JSOp) kw->op;
-	        RETURN(kw->tokentype);
-	    }
+            kw = &keywords[atom->kwindex];
+            tp->t_op = (JSOp) kw->op;
+            RETURN(kw->tokentype);
+        }
 	tp->t_op = JSOP_NAME;
 	tp->t_atom = atom;
 	RETURN(TOK_NAME);