Minor fixes / changes for Mac compatibility.
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index c50b35a..527b062 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -763,7 +763,7 @@
 		last_name_object = newstringobject(key);
 		if (last_name_object == NULL) {
 			last_name_char = NULL;
-			return NULL;
+			return -1;
 		}
 		last_name_char = key;
 	}
@@ -780,7 +780,7 @@
 		last_name_object = newstringobject(key);
 		if (last_name_object == NULL) {
 			last_name_char = NULL;
-			return NULL;
+			return -1;
 		}
 		last_name_char = key;
 	}
diff --git a/Objects/listobject.c b/Objects/listobject.c
index b51e3d8..38829e2 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -442,7 +442,7 @@
 {
 	if (!is_listobject(a)) {
 		err_badcall();
-		return NULL;
+		return -1;
 	}
 	return list_ass_slice((listobject *)a, ilow, ihigh, v);
 }
diff --git a/Objects/mappingobject.c b/Objects/mappingobject.c
index c50b35a..527b062 100644
--- a/Objects/mappingobject.c
+++ b/Objects/mappingobject.c
@@ -763,7 +763,7 @@
 		last_name_object = newstringobject(key);
 		if (last_name_object == NULL) {
 			last_name_char = NULL;
-			return NULL;
+			return -1;
 		}
 		last_name_char = key;
 	}
@@ -780,7 +780,7 @@
 		last_name_object = newstringobject(key);
 		if (last_name_object == NULL) {
 			last_name_char = NULL;
-			return NULL;
+			return -1;
 		}
 		last_name_char = key;
 	}