diff --git a/platform/darwin/string_nsstring.mm b/platform/darwin/string_nsstring.mm
index 9b1dc745c..ef6b96062 100644
--- a/platform/darwin/string_nsstring.mm
+++ b/platform/darwin/string_nsstring.mm
@@ -7,14 +7,20 @@ namespace platform {
 
 std::string uppercase(const std::string &string) {
     NSString *nsstring = [[NSString alloc] initWithBytesNoCopy:const_cast<char *>(string.data()) length:string.size() encoding:NSUTF8StringEncoding freeWhenDone:NO];
-    nsstring = [nsstring uppercaseString];
-    return { [nsstring cStringUsingEncoding:NSUTF8StringEncoding], [nsstring lengthOfBytesUsingEncoding:NSUTF8StringEncoding] };
+    NSString *nsstring2 = [nsstring uppercaseString];
+    [nsstring release];
+    const std::string result { [nsstring2 cStringUsingEncoding:NSUTF8StringEncoding], [nsstring2 lengthOfBytesUsingEncoding:NSUTF8StringEncoding] };
+    [nsstring2 release];
+    return result;
 }
 
 std::string lowercase(const std::string &string) {
     NSString *nsstring = [[NSString alloc] initWithBytesNoCopy:const_cast<char *>(string.data()) length:string.size() encoding:NSUTF8StringEncoding freeWhenDone:NO];
-    nsstring = [nsstring lowercaseString];
-    return { [nsstring cStringUsingEncoding:NSUTF8StringEncoding], [nsstring lengthOfBytesUsingEncoding:NSUTF8StringEncoding] };
+    NSString *nsstring2 = [nsstring lowercaseString];
+    [nsstring release];
+    const std::string result { [nsstring2 cStringUsingEncoding:NSUTF8StringEncoding], [nsstring2 lengthOfBytesUsingEncoding:NSUTF8StringEncoding] };
+    [nsstring2 release];
+    return result;
 }
 
 }