Index: src/runtime/lookup.m
==================================================================
--- src/runtime/lookup.m
+++ src/runtime/lookup.m
@@ -37,11 +37,12 @@
 class_respondsToSelector(Class cls, SEL sel)
 {
 	if (cls == Nil)
 		return NO;
 
-	return (objc_sparsearray_get(cls->dtable, sel->uid) != NULL ? YES : NO);
+	return (objc_sparsearray_get(cls->dtable, (uint32_t)sel->uid) != NULL
+	    ? YES : NO);
 }
 
 #if !defined(__ELF__) || (!defined(OF_X86_ASM) && !defined(OF_AMD64_ASM))
 static id
 nil_method(id self, SEL _cmd)
@@ -55,11 +56,13 @@
 	IMP imp;
 
 	if (obj == nil)
 		return (IMP)nil_method;
 
-	if ((imp = objc_sparsearray_get(obj->isa->dtable, sel->uid)) == NULL)
+	imp = objc_sparsearray_get(obj->isa->dtable, (uint32_t)sel->uid);
+
+	if (imp == NULL)
 		return objc_forward_handler(obj, sel);
 
 	return imp;
 }
 
@@ -69,13 +72,13 @@
 	IMP imp;
 
 	if (super->self == nil)
 		return (IMP)nil_method;
 
-	imp = objc_sparsearray_get(super->class->dtable, sel->uid);
+	imp = objc_sparsearray_get(super->class->dtable, (uint32_t)sel->uid);
 
 	if (imp == NULL)
 		return objc_forward_handler(super->self, sel);
 
 	return imp;
 }
 #endif

Index: src/runtime/selector.m
==================================================================
--- src/runtime/selector.m
+++ src/runtime/selector.m
@@ -103,11 +103,11 @@
 sel_getName(SEL sel)
 {
 	const char *ret;
 
 	objc_global_mutex_lock();
-	ret = objc_sparsearray_get(selectors, sel->uid);
+	ret = objc_sparsearray_get(selectors, (uint32_t)sel->uid);
 	objc_global_mutex_unlock();
 
 	return ret;
 }
 

Index: src/runtime/sparsearray.m
==================================================================
--- src/runtime/sparsearray.m
+++ src/runtime/sparsearray.m
@@ -26,11 +26,11 @@
 static struct objc_sparsearray_level3 *empty_level3 = NULL;
 
 static void
 init(void)
 {
-	size_t i;
+	uint_fast16_t i;
 
 	empty_level2 = malloc(sizeof(struct objc_sparsearray_level2));
 	empty_level3 = malloc(sizeof(struct objc_sparsearray_level3));
 
 	if (empty_level2 == NULL || empty_level3 == NULL)
@@ -47,11 +47,11 @@
 
 struct objc_sparsearray*
 objc_sparsearray_new(void)
 {
 	struct objc_sparsearray *s;
-	size_t i;
+	uint_fast16_t i;
 
 	if (empty_level2 == NULL || empty_level3 == NULL)
 		init();
 
 	if ((s = malloc(sizeof(struct objc_sparsearray))) == NULL)
@@ -65,11 +65,11 @@
 
 void
 objc_sparsearray_copy(struct objc_sparsearray *dst,
     struct objc_sparsearray *src)
 {
-	size_t i, j, k;
+	uint_fast16_t i, j, k;
 	uint32_t idx;
 
 	for (i = 0; i < 256; i++) {
 		if (src->buckets[i]->empty)
 			continue;
@@ -100,11 +100,11 @@
 	uint8_t j = idx >>  8;
 	uint8_t k = idx;
 
 	if (s->buckets[i]->empty) {
 		struct objc_sparsearray_level2 *t;
-		size_t l;
+		uint_fast16_t l;
 
 		t = malloc(sizeof(struct objc_sparsearray_level2));
 
 		if (t == NULL)
 			ERROR("Not enough memory to insert into sparse array!");
@@ -117,11 +117,11 @@
 		s->buckets[i] = t;
 	}
 
 	if (s->buckets[i]->buckets[j]->empty) {
 		struct objc_sparsearray_level3 *t;
-		size_t l;
+		uint_fast16_t l;
 
 		t = malloc(sizeof(struct objc_sparsearray_level3));
 
 		if (t == NULL)
 			ERROR("Not enough memory to insert into sparse array!");
@@ -138,11 +138,11 @@
 }
 
 void
 objc_sparsearray_free(struct objc_sparsearray *s)
 {
-	size_t i, j;
+	uint_fast16_t i, j;
 
 	for (i = 0; i < 256; i++) {
 		if (s->buckets[i]->empty)
 			continue;