diff --git a/dtable.c b/dtable.c
index e96702f..a0f6c47 100644
--- a/dtable.c
+++ b/dtable.c
@@ -88,7 +88,7 @@ static void collectMethodsForMethodListToSparseArray(
 	}
 	for (unsigned i=0 ; i<list->count ; i++)
 	{
-		SparseArrayInsert(sarray, (uint32_t)list->methods[i].selector->sel_id,
+		SparseArrayInsert(sarray, PTR_TO_IDX(list->methods[i].selector->sel_id),
 				(void*)&list->methods[i]);
 	}
 }
@@ -99,7 +99,7 @@ static BOOL installMethodInDtable(Class class,
                                   BOOL replaceExisting)
 {
 	assert(__objc_uninstalled_dtable != dtable);
-	uint32_t sel_id = (uint32_t)method->selector->sel_id;
+	uint32_t sel_id = PTR_TO_IDX(method->selector->sel_id);
 	struct objc_slot *slot = SparseArrayLookup(dtable, sel_id);
 	if (NULL != slot && slot->owner == class)
 	{
diff --git a/sarray2.h b/sarray2.h
index 8a1a6a1..5c99969 100644
--- a/sarray2.h
+++ b/sarray2.h
@@ -117,4 +117,6 @@ void * SparseArrayNext(SparseArray * sarray, uint32_t * index);
  */
 SparseArray *SparseArrayCopy(SparseArray * sarray);
 
+#define PTR_TO_IDX(x) ((uint32_t)(uintptr_t)x)
+
 #endif //_SARRAY_H_INCLUDED_
diff --git a/sendmsg.c b/sendmsg.c
index 6d232cf..93c10e5 100644
--- a/sendmsg.c
+++ b/sendmsg.c
@@ -36,8 +36,6 @@ static mutex_t initialize_lock;
 
 void objc_resolve_class(Class);
 
-#define sidx uint32_t
-
 /* Two hooks for method forwarding. If either is set, it is invoked
  * to return a function that performs the real forwarding.  If both
  * are set, the result of __objc_msg_forward2 will be preferred over
@@ -194,7 +192,7 @@ objc_msg_lookup (id receiver, SEL op)
   if (receiver)
     {
       result = sarray_get_imp (receiver->class_pointer->dtable, 
-                                (sidx)op->sel_id);
+                                PTR_TO_IDX(op->sel_id));
       if (result == 0)
         {
           /** Get the dtable that we should be using for lookup.  This will
@@ -218,7 +216,7 @@ objc_msg_lookup (id receiver, SEL op)
                  has been installed by another thread after we did the
                  previous check that the method exists).
               */
-              result = sarray_get_imp (dtable, (sidx)op->sel_id);
+              result = sarray_get_imp (dtable, PTR_TO_IDX(op->sel_id));
               if (result == 0)
                 {
                   /* Try again after giving the code a chance to install new
diff --git a/sendmsg2.c b/sendmsg2.c
index 6d1974b..f205854 100644
--- a/sendmsg2.c
+++ b/sendmsg2.c
@@ -22,7 +22,7 @@ static inline
 Slot_t objc_msg_lookup_internal(id *receiver, SEL selector, id sender)
 {
 	Slot_t result = sarray_get_safe((*receiver)->class_pointer->dtable,
-			(sidx)selector->sel_id);
+			PTR_TO_IDX(selector->sel_id));
 	if (0 == result)
 	{
 		Class class = (*receiver)->class_pointer;
@@ -32,7 +32,7 @@ Slot_t objc_msg_lookup_internal(id *receiver, SEL selector, id sender)
 		{
 			__objc_init_install_dtable (*receiver, selector);
 			dtable = dtable_for_class(class);
-			result = sarray_get_safe(dtable, (sidx)selector->sel_id);
+			result = sarray_get_safe(dtable, PTR_TO_IDX(selector->sel_id));
 			if (0 == result)
 			{
 				objc_mutex_lock(__objc_runtime_mutex);
@@ -43,14 +43,14 @@ Slot_t objc_msg_lookup_internal(id *receiver, SEL selector, id sender)
 					dtable = dtable_for_class(class);
 				}
 				objc_mutex_unlock(__objc_runtime_mutex);
-				result = sarray_get_safe(dtable, (sidx)selector->sel_id);
+				result = sarray_get_safe(dtable, PTR_TO_IDX(selector->sel_id));
 			}
 		}
 		else
 		{
 			// Check again incase another thread updated the dtable while we
 			// weren't looking
-			result = sarray_get_safe(dtable, (sidx)selector->sel_id);
+			result = sarray_get_safe(dtable, PTR_TO_IDX(selector->sel_id));
 		}
 		if (0 == result)
 		{
@@ -117,7 +117,8 @@ Slot_t objc_slot_lookup_super(Super_t super, SEL selector)
 	if (receiver)
 	{
 		Class class = super->class;
-		Slot_t result = sarray_get_safe(dtable_for_class(class), (sidx)selector->sel_id);
+		Slot_t result = sarray_get_safe(dtable_for_class(class),
+				PTR_TO_IDX(selector->sel_id));
 		if (0 == result)
 		{
 			// Dtable should always be installed in the superclass