diff --git a/README.md b/README.md
index 67f2912..937340a 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,10 @@ USAGE
                                             [weakSelf doSomething];
                                           }];
 
+REQUIREMENTS
+============
+RNTimer uses ARC. If your project doesn’t, set the `-fobjc-arc` flag for `RNTimer.m`.
+
 BACKGROUND
 ==========
 http://robnapier.net/blog/simple-gcd-timer-rntimer-762
\ No newline at end of file
diff --git a/RNTimer/RNTimer.m b/RNTimer/RNTimer.m
index cc1b180..585d5b1 100644
--- a/RNTimer/RNTimer.m
+++ b/RNTimer/RNTimer.m
@@ -24,12 +24,12 @@
 //  DEALINGS IN THE SOFTWARE.
 //
 
-
 #import "RNTimer.h"
+#import <Availability.h>
 
 @interface RNTimer ()
 @property (nonatomic, readwrite, copy) dispatch_block_t block;
-@property (nonatomic, readwrite, assign) dispatch_source_t source;
+@property (nonatomic, readwrite, strong) dispatch_source_t source;
 @end
 
 @implementation RNTimer
@@ -58,7 +58,10 @@ + (RNTimer *)repeatingTimerWithTimeInterval:(NSTimeInterval)seconds
 - (void)invalidate {
   if (self.source) {
     dispatch_source_cancel(self.source);
+	  
+#if __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_6_0
     dispatch_release(self.source);
+#endif
     self.source = nil;
   }
   self.block = nil;