diff --git a/js/ref/jsapi.c b/js/ref/jsapi.c
index 5cdd9cb1bb5..24724a4796e 100644
--- a/js/ref/jsapi.c
+++ b/js/ref/jsapi.c
@@ -1201,19 +1201,11 @@ JS_DefineConstDoubles(JSContext *cx, JSObject *obj, JSConstDoubleSpec *cds)
 	 * so we don't need to GC-alloc constant doubles.
 	 */
 	jsdouble d = cds->dval;
+        jsint i;
 
-        /* We can't do a (jsint) cast to check against JSDOUBLE_IS_INT until we
-         * know that d is not NaN, or we risk a FPE on some platforms.
-         */
-        if (JSDOUBLE_IS_NaN(d) || !JSDOUBLE_IS_FINITE(d)) {
-            value = DOUBLE_TO_JSVAL(&cds->dval);
-        } else {
-            jsint i = (jsint)d;
-
-            value = (JSDOUBLE_IS_INT(d, i) && INT_FITS_IN_JSVAL(i))
-		? INT_TO_JSVAL(i)
-		: DOUBLE_TO_JSVAL(&cds->dval);
-        }
+        value = (JSDOUBLE_IS_INT(d, i) && INT_FITS_IN_JSVAL(i))
+            ? INT_TO_JSVAL(i)
+            : DOUBLE_TO_JSVAL(&cds->dval);
 #else
 	ok = js_NewNumberValue(cx, cds->dval, &value);
 	if (!ok)
diff --git a/js/ref/jsemit.c b/js/ref/jsemit.c
index 8c5cbc0a2e3..caed6742282 100644
--- a/js/ref/jsemit.c
+++ b/js/ref/jsemit.c
@@ -397,7 +397,6 @@ EmitNumberOp(JSContext *cx, jsdouble dval, JSCodeGenerator *cg)
     JSAtom *atom;
     JSAtomListElement *ale;
 
-    ival = (jsint)dval;
     if (JSDOUBLE_IS_INT(dval, ival) && INT_FITS_IN_JSVAL(ival)) {
 	if (ival == 0)
 	    return js_Emit1(cx, cg, JSOP_ZERO) >= 0;
diff --git a/js/ref/jsinterp.c b/js/ref/jsinterp.c
index 8873a00c111..08d91f936bd 100644
--- a/js/ref/jsinterp.c
+++ b/js/ref/jsinterp.c
@@ -140,7 +140,6 @@ static JSClass prop_iterator_class = {
 	jsint _i;                                                             \
 	jsval _v;                                                             \
 									      \
-	_i = (jsint)d;                                                        \
 	if (JSDOUBLE_IS_INT(d, _i) && INT_FITS_IN_JSVAL(_i)) {                \
 	    _v = INT_TO_JSVAL(_i);                                            \
 	} else {                                                              \
diff --git a/js/ref/jsnum.c b/js/ref/jsnum.c
index a887f9a5804..376e144c4e7 100644
--- a/js/ref/jsnum.c
+++ b/js/ref/jsnum.c
@@ -393,7 +393,6 @@ js_NewNumberValue(JSContext *cx, jsdouble d, jsval *rval)
 {
     jsint i;
 
-    i = (jsint)d;
     if (JSDOUBLE_IS_INT(d, i) && INT_FITS_IN_JSVAL(i)) {
 	*rval = INT_TO_JSVAL(i);
     } else {
@@ -427,7 +426,6 @@ js_NumberToString(JSContext *cx, jsdouble d)
     jsint i;
     char buf[32];
 
-    i = (jsint)d;
     if (JSDOUBLE_IS_INT(d, i)) {
 	PR_snprintf(buf, sizeof buf, "%ld", (long)i);
     } else {
diff --git a/js/ref/jsnum.h b/js/ref/jsnum.h
index 626a6b478ad..bee89f49dd3 100644
--- a/js/ref/jsnum.h
+++ b/js/ref/jsnum.h
@@ -57,14 +57,14 @@ PR_BEGIN_EXTERN_C
 #define JSDOUBLE_IS_NEGZERO(d)  (JSDOUBLE_HI32(d) == JSDOUBLE_HI32_SIGNBIT && \
 				 JSDOUBLE_LO32(d) == 0)
 
-#define JSDOUBLE_IS_INT_2(d, i)	(!JSDOUBLE_IS_NEGZERO(d) && (jsdouble)i == d)
-
-#ifdef XP_PC
-/* XXX MSVC miscompiles NaN floating point comparisons for ==, !=, <, and <= */
-#define JSDOUBLE_IS_INT(d, i)	(!JSDOUBLE_IS_NaN(d) && JSDOUBLE_IS_INT_2(d, i))
-#else
-#define JSDOUBLE_IS_INT(d, i)	JSDOUBLE_IS_INT_2(d, i)
-#endif
+/*
+ * JSDOUBLE_IS_INT first checks that d is neither NaN nor infinite, to avoid
+ * raising SIGFPE on platforms such as Alpha Linux, then (only if the cast is
+ * safe) leaves i as (jsint)d.  This also avoid anomalous NaN floating point
+ * comparisons under MSVC.
+ */
+#define JSDOUBLE_IS_INT(d, i) (JSDOUBLE_IS_FINITE(d) && !JSDOUBLE_IS_NEGZERO(d) \
+                               && ((d) == (i = (jsint)(d))))
 
 /* Initialize the Number class, returning its prototype object. */
 extern JSObject *