diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0dd7124..3ec843f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,8 @@
 ## master
 * Add your own contributions to the next release on the line below this with your name.
 
+- [fix] Fix group can add operations and set completion multiple times when the group start. [#22](https://github.com/pinterest/PINOperation/pull/22)
+
 ## 1.1.1 -- 2018 February 3
 * Cleanup warnings [garrett](https://github.com/garrettmoon)
 
diff --git a/Source/PINOperationGroup.m b/Source/PINOperationGroup.m
index ddd2ed0..98539e9 100644
--- a/Source/PINOperationGroup.m
+++ b/Source/PINOperationGroup.m
@@ -76,6 +76,7 @@ - (void)start
   [self lock];
     NSAssert(_canceled == NO, @"Operation group canceled.");
     if (_started == NO && _canceled == NO) {
+      _started = YES;
       for (NSUInteger idx = 0; idx < _operations.count; idx++) {
         dispatch_group_enter(_group);
         dispatch_block_t originalOperation = _operations[idx];
@@ -167,6 +168,7 @@ - (void)runCompletionIfNeeded
   [self lock];
     completion = _completion;
     _completion = nil;
+    _started = NO;
   [self unlock];
 
   if (completion) {